Skip to main content

Full text of "Laboratory projects in physics, a manual of practical experiments for beginners"

See other formats


BOMIWY PROJECT 

IN PHYSICS 

GOOD 



LABORATORY PROJECTS IN PHYSICS 



THE MACMILLAN COMPANY 

NEW YORK BOSTON CHICAGO DALLAS 
ATLANTA SAN FRANCISCO 

MACMTLLAN & CO., LIMITED 

LONDON BOMBAY CALCUTTA 
MELBOURNE 

THE MACMILLAN CO. OF CANADA, LTD. 

TORONTO 



V 

G,. 

LABORATORY PROJECTS IN 
PHYSICS 

A MANUAL OF PRACTICAL EXPERI- 
MENTS FOR BEGINNERS 



BY 



FREDERICK F.' GOOD, A. M. 

INSTRUCTOR IN THE SCHOOL OF PRACTICAL ARTS 

AND IN THE SCHOOL OF EDUCATION 

COLUMBIA UNIVERSITY 

NEW YORK CITY 



Illustrations by B. F. Williamson 

II 




Nefo 

THE MACMILLAN COMPANY 
1921 

All rights reserved 



COPYRIGHT, 1920, 
BY THE MACMILLAN COMPANY. 



Set up and clectrotyped. Published October, 1920. 



Nortooot) ^rtss 

J. S. Gushing Co. Berwick & Smith Co. 
Norwood, Mass., U.S.A. 



PREFACE 

THESE experiments have been organized for the purpose of giving 
concrete expression, in the field of physics, to the recent tendencies 
in the teaching of science with respect to aim, subject matter, and 
method. The physics course in a modern high school should be 
organized according to the recognized function of education in a 
democratic society. It should include units of study which the 
masses of boys and girls of high school age are able to pursue with 
profit. It should proceed toward an organization of practical 
situations, activities, and phenomena, the value of which will be 
recognized and approved by teachers, students, parents, adminis- 
trators of education, and others who are responsible for the work 
which boys and girls do in the high school. 

It is intended that these experiments should form part of a physics 
course which includes class discussions and demonstrations. They 
were devised and used for several years in a beginners' course in 
practical physics. They differ from the conventional physics 
laboratory experiments in that they deal more directly with the 
mechanisms and appliances of everyday experience. The ma- 
terials and procedure have been worked out in detail in order to 
aid the busy science teacher in the laborious task of placing prac- 
tical laboratory study upon a workable basis. 

A large list of projects and problems is offered. In a year's 
course of thirty-six to forty weeks perhaps not more than half of 
the ninety-five experiments can be performed. The complete list 
represents two years' work unless more time is assigned to labo- 
ratory study than is the custom. Obviously the purpose of so large 
a list is to provide for optional work,, especially in Groups II-III, 



VI PREFACE 

to suit the individual needs, purposes, and inclinations of boys 
and girls of high school age. 

The experiments are divided into three groups representing dif- 
ferent types of practical work suited to varying requirements in 
difficulty and varying conditions in laboratory equipment. 

Group I experiments require inexpensive apparatus. These 
experiments are designed to develop skill in assembling and in 
manipulation as well as to provide a fund of simple introductory 
exercises dealing with important practical subject matter. One 
complete set of apparatus for all experiments in Group I costs 
fifty to seventy-five dollars. A complete list of apparatus may 
be found in the appendix. It includes names and addresses of 
dealers who can supply the materials. 

In the author's classes, students are required to work individually 
on Group I experiments for the purpose of developing self-reliance 
and individual skill. In Groups II-III students may work in pairs. 
They do not, as a rule, work in larger groups. Laboratory sections 
with one instructor are limited, whenever possible, to a maximum of 
twenty students. For a class of twenty students at least five com- 
plete sets of Group I apparatus are provided with some additional 
parts to replace loss due to breakage. Half of the class, Division A 
(ten students), work on Group I experiments; the other half, Divi- 
sion B (ten students), work on Group II experiments. At the next 
session of the laboratory work Divisions A and B alternate, Divi- 
sion B working on Group I and Division A working on Group II. 
In Groups II-III students are permitted to make their own choice 
of experiments. In using this scheme it is advisable that apparatus 
parts for several different Group I experiments be placed on a con- 
venient center table in the laboratory. 

During the year's course in laboratory work students are re- 
quired to do all or nearly all the experiments in Group I and not 
less than fifteen experiments in Groups II-III. In general, Group 
III experiments are more difficult than those of Group II, requiring 
more laboratory practice and more preliminary study. Students 






PREFACE vii 

are not permitted to choose Group III experiments until the second 
half of the course except in cases of special ability. Students who 
do more work than the minimum requirement set by the teacher 
may receive additional credit. Approximately half as much time 
is required for doing a Group I experiment as for a Group II-III 
experiment. The time assigned for a laboratory session in this 
work should be not less than two consecutive forty-minute periods. 
In this time students are able to do, on the average, two Group I 
experiments or one to two Group II-III experiments. One double- 
period laboratory session each week is a common practice. In 
some schools it may be found advisable to extend this time. 

In the author's laboratory, apparatus parts for Group I experi- 
ments are stored in a cabinet of numbered drawers of dimensions 
(inside) 4 inches high by 4^ inches wide by 13 inches long. A 
cabinet containing from twenty-four to forty-eight drawers should 
be provided for this purpose. An index is made showing exactly 
where materials may be found. Materials of this kind must be 
properly organized to avoid confusion and inefficiency. 

Apparatus for Groups II-III may be stored in cabinets located 
at the sides of the laboratory, easily accessible to students. This 
material may be kept in a cabinet of twelve to twenty-four com- 
partments with hinged doors. The compartments are of size 18 
inches wide by 21 inches high by 18 inches deep, inside measure- 
ments. For manufacturers of cabinets see apparatus list in the 
appendix. For convenience in locating apparatus, all cabinets 
must be properly numbered and indexed with the title of the ex- 
periment. Students are expected to take apparatus from the 
cabinets to the laboratory tables and return it in proper order to 
the cabinet when the experiment is finished. 

The course involves the use of a workable laboratory reference 
shelf in connection with the experimental studies. References are 
made to specific books. See reference book list, page 247. 

A large list of books for special study, reference, and general 
reading will be found in the appendix. Many of these books deal 



Vlll PREFACE 

with informational, historical, and biographical phases of science 
in an absorbingly interesting manner and should provide a valu- 
able fund of supplementary reading. 

The author is deeply obligated to many teachers and students 
of Teachers College for their cooperation and assistance. Special 
acknowledgment is due to Professor John F. Woodhull for his 
many helpful suggestions and criticisms and to the following men 
who assisted with the details of organization and instruction : Mr. 
George D. von Hofe, Mr. George Schantin, Mr. Donald H. Wilson, 
Mr. Morris Meister, Mr. John Bryan, Mr. Simon Brandstadter, 
and Mr. Murray J. Etkin. The following individuals contributed 
generously either in reading the manuscript or in testing the ex- 
periments with their classes : Dr. Otis W. Caldwell, Director of 
the Lincoln School; Professor May B. van Arsdale of Teachers 
College ; Mr. Roland H. Williams, formerly of the Horace Mann 
School for Boys, now of the Scarborough School; Mr. Alton I. 
Lockhart of the Horace Mann School for Girls ; Mr. Arthur L. 
Yoder of the Richmond Hill High School, Brooklyn ; Miss Mabel 
T. Rogers of the Georgia Normal and Industrial College; and 
Mr. C. N. Adkisson of the Texas College of Industrial Arts. 
The author is especially indebted to Mr. Raymond B. Brownlee 
of the Stuyvesant High School, New York City, for his careful 
reading of the manuscript and for many valuable suggestions. 



DIRECTIONS FOR STUDENTS 

AT the first laboratory session the class will be divided into two 
sections. Section A will work on Group I experiments, and Sec- 
tion B on Group II experiments. At the next laboratory ses- 
sion the sections will alternate, Section B working on Group I 
experiments and Section A on Group II, etc. The apparatus 
required for Group I experiments will be found in boxes on a lab- 
oratory table. For Groups II-III experiments the apparatus will 
be found in cabinets unless other provision for storing this material 
is made. 

Students should work individually on Group I experiments. 
Much of the value to be gained from this study will depend upon 
whether you can improve your ability to put mechanical parts to- 
gether, make them work, understand what the different parts do, 
find out what is wrong if they do not work properly, correct the 
trouble, and learn the principles of their operation. Before begin- 
ning an experiment read the directions carefully. Examine the 
illustrations and, if necessary, the model of the apparatus made by 
the teacher. Note the special positions of clamps and rings in 
holding glassware to avoid breaking. Then proceed to the appa- 
ratus table, get the necessary parts, set up your own apparatus, and 
make it work properly. When each experiment is finished, you 
are expected to disassemble the apparatus and place the parts 
in the proper boxes. Your place at the laboratory tables should 
always be left in good order. 

In doing experiments from Groups II-III, students may work in 
pairs (not in larger groups). In general, experiments from Group 
III are more difficult and should not be selected till the second 



X DIRECTIONS FOR STUDENTS 

half of the course. When you have selected an experiment, write 
its title with your name on a slip of paper and have the instructor 
approve the slip. This entitles you to the use of the apparatus. 
If any of the required materials are not found in the proper cabinet, 
write the names of the articles needed on your " approval slip" 
and give it to the instructor. He will then give you the apparatus. 
When the experiment is finished, return the special apparatus per- 
sonally to the instructor and get your " approval slip" from him 
as a receipt for its return. 

For directions regarding laboratory reports see page i . 



CONTENTS 

PAGE 

GROUP I. EXPERIMENTS 

1. The Lift Pump 2 

2. The Force Pump ......... 4 

3. The Pendulum 6 

4. The Clock 8 

5. Measuring Liquid Pressures . . . . . . .11 

6. Measuring Gas Pressure . . .14 

7. The Hydraulic Elevator 16 

8. Floating Bodies . . ' . . . . . . .18 

9. The Hydrometer 20 

10. The Siphon .......... 22 

11. The Siphon Fountain 24 

12. Pressure Tank Water Supply Boyle's Law .... 25 

13. Faucet Water Pressure Boyle's Law ..... 28 

14. Steam Heating System 30 

15. Heat of Condensation (or Vaporization) Latent Heat . . 33 

16. Hot Water Heating System 36 

17. Heat of Fusion Latent Heat 38 

1 8. Kitchen Hot Water Tank 41 

19. The Liquid Cell and the Dry Cell 43 

20. Measuring Electric Current 46 

21. Electric Light and Power 48 

22. Electromagnets and Permanent Magnets . . . .51 

23. The Electric Bell and the Telegraph 53 

24. Electroplating . . . . . . . . . -55 

25. Pin-hole Images . . 58 

26. Lens Images .......... 60 

27. Law of Reflection ......... 62 

28. The Law of Intensity . 64 

29. The Prism and the Lens-Refraction ..... 66 

30. The Glass Cube and the Lens Refraction .... 69 

31. Illumination and Lighting . . . . . . .72 

32. Candle-power and Foot-candles 74 



xii CONTENTS 



33. 


Color 


PAGE 

76 


oo* 

34. 


Absorption and Lighting .... 


. 78 


35- 


Tuning Fork and Vibrating Air Column . 


. 80 


36. 


The Vibrating String .... 


. . . . 83 


GROUP 


II. EXPERIMENTS 




37- 


Blood Pressure 


. 86 


38. 


The Camera A 


. . . . 89 


39- 


Electric Motor A 


. 92 


40. 


The Fireless Cooker Insulators 


. 95 


41. 


The Gas Stove Burner .... 


. . . . 98 


42. 


Gasoline Engine A 


. 100 


43- 


Heating a Room Cost A . 


. 103 


44- 


Heating a Room Cost B . 


. 105 


45- 


House Gas Supply City Gas 


. 107 


46. 


House Water Supply .... 


. no 


47- 


The Dew Point 


. 112 


48. 


The Jack Screw ..... 


. . . .114 


49- 


The Kerosene Stove .... 


. 116 


5. 


Levers and Scales ..... 


. ' . 118 


5i. 


The Microscope Simple and Compound 


. 121 


52. 


The Optical Disk 


. . 1^5 


53- 


The Pressure Cooker .... 


. 127 


54. 


The Phonograph A 


. I2 9 


55- 


Projection Lantern A . 


. 133 


56. 


The Pulley 


135 


57- 


The Pump Kitchen Lift Pump 


. . -137 


58. 


Saucepan Conduction .... 


. 139 


59- 


Sewing Machine A 


. 140 


60. 


Water Motor A . . 


. 143 


GROUP 


III. EXPERIMENTS 


' 


61. 


Alternating Currents 


. 145 


62. 


Camera B 


. . . . I 4 8 


63. 


Camera C 


. 150 


64. 


The Electric Disk Stove .... 


. 154 


6c 




I<6 


0" 

66. 


The Electric Immersion Heater 


. 158 


67. 


Electric Motor B 


. 160 



CONTENTS xiii 





PAGE 

. 163 


60 Horse Power A Electric Motor 


164 


70. Horse Power B 


. ' . . .167 


71. Humidity A ..... 


168 




. 170 


73. Phonograph B 


173 




. 175 


75. Rheostat and Electrical Resistance . 


. .177 


76. Sewing Machine B 


i79 




. 182 


78. Telephone A 


185 


79. Telephone B 


187 


80. The Telescope 


ioo 


81. The Thermometer .... 


iQ4 


82. The Vacuum Cleaner 


198 


83. Water Heater Gas 


200 


84. Water Motor B . . . 


203 


85. Wireless A 


206 


86. Wireless B 


210 


AUTOMOBILE WORK 




87. Carburetor A 


216 


88. Carburetor B .... 


219 


89. Ford Engine A 


222 


90. Ford Engine B 


227 


91. Ignition Systems A Simple 


. 23O 


92. Ignition Systems B 


232 


93. Ignition Systems C, Ford Ignition 


235 


94. Storage Battery A 


240 


95. Storage Battery B 


243 


APPENDIX 




Laboratory Reference Shelf 


247 


Books for Reference and Reading 


2 4 8 




. 253 


Cabinets for Apparatus .... 


267 


Electric Wiring for the Laboratory , 


267 



LABORATORY PROJECTS IN 
PHYSICS 



GROUP I. EXPERIMENTS 

A CAREFUL record of each experiment that is performed should be 
kept in a laboratory notebook (loose leaf). Write the title of the 
experiment, your name, and the date at the top of each report. 
Answer questions in complete sentences, make diagrams, and record 
data and explanations according to the numbering in the direc- 
tions. Make diagrams of apparatus whenever possible. They 
will help you to understand and remember the important facts of 
the experiment. Your laboratory report should show to the in- 
structor at a glance whether or not you understood what you were 
doing. It should also help you to review the experiment for a test 
with the least loss of time. 

Laboratory reports should be handed in at the next period after 
the experiment is completed. If you have extra time during the 
laboratory period, it should be spent in writing up reports, in doing 
reference work, or in planning for the next experiment. 

Furthur suggestions relating to the organization of class proce- 
dure and to the emphasis upon fundamental mechanical skills will 
be found under Directions to Students, page x. 



LABORATORY PROJECTS IN PHYSICS 



i. THE LIFT PUMP 

To construct a lift pump and explain its action. 

MATERIALS. No. 50 Macbeth chimney ; i2-oz. bottle; 12 -in., solid brass 
piston rod, diameter 6 mm., with cotter pins ; i2-in. glass tube, outside diameter 
7 mm. ; No. 7 one-hole stopper ; No. 6 two-hole stopper (one hole at center) ; 
thin leather sheeting and tacks. 




FIG. i. A lift pump. 



THE LIFT PUMP 3 

The Lift Pump. Fit stoppers into the glass cylinders to con- 
struct a lift pump. See model made by the instructor. (Cau- 
tion. Do not clamp the sides of a glass chimney, as it is easily 
broken.} Special care should be exercised in fitting the piston and 
in making the valves. The piston should move easily inside the 
cylinder when wet. It should not be so loose as to allow leakage. 
Make the leather valves large enough to completely cover the 
passageways. The valves should be fastened with ordinary carpet 
tacks. When parts are properly fitted, test the apparatus for lift- 
ing water. It may be necessary to pour a little water into the 
upper part of the cylinder. 

1. Describe the action of the valves. What is the function of 
the foot valve ? the piston valve ? 

2. What causes the water to rise from the cistern when the piston 
is raised ? Refer to texts under pumps. See Black and Davis. 

3. What is meant by the statement that a pump sucks water? 
Is this expression a correct one? 

4. Can you explain why the pump works better after water 
reaches the cylinder? 

5. What is meant by priming an old pump? See Carhart and 
Chute. 

6. Why must the piston valve in a lift pump be less than 34 feet * 
above the water surface? See any textbook. Refer to pumps. 

7. Make two diagrams, one showing the position of the valves 
as the piston goes up and one as the piston goes down. 

8. Name four different kinds of pumps and state what each is 
used for. Refer to textbooks. 

The action of this pump is similar to that of the kitchen lift 
pump, Experiment No. 5" Examine the parts of this pump 
if the apparatus is in the la, oratory. 

BOOKS FOR SPECIAL STUDY: 
General Science Barber. 
Home Water Works Lynde. 
Household Physics Butler. 



LABORATORY PROJECTS IN PHYSICS 



2. THE FORCE PUMP 

To construct a force pump and explain its action. 

MATERIALS. Chimney; 3 bottles; brass rod; glass tube i2-in.; 3 glass 
tubes 4-in. ; nozzle tube 4-in. ; No. 6 stopper, one-hole ; 2 No. 7 stoppers, two- 
holes; leather sheeting and tacks; rubber tubing, 2 pieces, 12 in. 



-~A/'r Cushion 




- Va/ve 



We// 



FIG. 2. An air cushion force pump. 



THE FORCE PUMP 5 

The Force Pump. Make an air-chamber force pump, using a 
twelve-ounce bottle for the air chamber. See instructor's model. 
After fitting all stoppers firmly to withstand pressure, support the 
apparatus on a ring stand and operate as a force pump. Note 
carefully how clamps and rings are placed to hold the cylinder 
and to prevent the stoppers from blowing out of the air chamber. 

1. What proof have you that the air in the bottle acts as a 
cushion? Air cushions are frequently used on water pipes to 
protect them from sudden pressure strains. 

2. What effect has the air cushion upon the flow of the water? 
Fire engines and large pumps employ large metallic domes for 
this purpose. Faucets are sometimes equipped with small air 
cushions to prevent hammering in the pipe when the faucet closes 
suddenly. An air cushion also forms part of the construction of a 
hydraulic ram. 

3. How does the piston of the force pump differ from that of 
the lift pump? 

4. What causes the water to flow steadily from the delivery 
nozzle ? 

5. Make a diagram of this force pump, showing the position of 
the valves as the piston goes up. 

6. Mention one practical situation in which a force pump would 
be used. 

7. What type of pump is used on fire engines? See Black and 
Davis. 

8. Is the human heart a " suction " pump or a force pump? 
Explain by a diagram. See Household Physics Butler. 

BOOKS FOR SPECIAL STUDY: 

General Science Barber. 
Physics Black and Davis. 
Home Water Works Lynde. 



LABORATORY PROJECTS IN PHYSICS 



3. THE PENDULUM 
To study the action of pendulums. 
MATERIALS. Thread and bobs; yardstick; ring stand; alarm clock. 




FIG. 3a. A pendulum. 





FIG. 3b. Clock escapement 
with pendulum. 



The Pendulum. Suspend a weight from a ringstand at the 
edge of a table by a thread four feet long. Measure from the 



THE PENDULUM 7 

point of suspension to the center of the weight. Allow it to swing 
through a small arc of about three inches and count the number 
of vibrations per minute. (Count over and back as one vibra- 
tion.) Repeat with a large arc (wider swing). 

1. How does varying the amplitude (arc) affect the number of 
vibrations per minute ? 

2. Double the weight and count the number of vibrations. 
(Suspend two weights side by side on one thread. Measure ac- 
curately four feet from the center of the weights to the point of 
support.) Does the weight of the pendulum affect the number 
of vibrations per minute? 

3. Repeat with pendulums one fourth and one ninth as long. 
How does the length of the pendulum affect the number of vibra- 
tions per minute? 

4. How do the number of vibrations per unit time of any two 
pendulums compare? See Hoadley. 

5. What is a seconds pendulum? See Carhart and Chute. 

As the force of gravity increases the number of vibrations per 
minute increases. The attraction of gravity increases slightly 
in the polar regions, due to the fact that the earth is not a perfect 
sphere. The number of vibrations is proportional to the square 
root of gravity. Therefore if the pull of gravity were four times 
as great the pendulum would vibrate twice as fast. If gravity 
were nine times as great the pendulum would vibrate three times 
as fast. If gravity were one fourth as great, the pendulum would 
vibrate one half as fast. 

6. If a pendulum clock, running accurately in New York, were 
taken North, what adjustment would have to be made in order 
to maintain the accuracy of the timepiece? 

7. The attraction of the sun is twenty-seven times as great as 
the attraction of the earth. If a seconds pendulum were taken 
from the earth to the sun, how fast would it vibrate ? The square 
root of 27 is 5.196. 



8 LABORATORY PROJECTS IN PHYSICS 

The attraction of gravity on the moon is one sixth as great as 
on the earth. The attraction of gravity on the planet Jupiter is 
two and one half times as great as on the earth. 

8. If a simple pendulum clock were taken from a cold room 
to a warm one, how would expansion affect its rate of movement? 
See Millikan, Gale and Pyle. Refer to index under Pendulum, 
compensated. 

BOOKS FOR SPECIAL STUDY: 

The Modern Clock Goodrich. 
Physics Millikan, Gale and Pyle. 



4. THE CLOCK 

To construct a clock and study its mechanism. 
MATERIALS. Tick-tack clock set. 

The Clock. Assemble the parts and operate the dissectible 
clock. There are three main parts to a clock or watch : 

a. The source of power (weight or spring). 

b. A train of wheels operated by the driving force. 

c. An agent for controlling the speed of the mechanism (pen- 
dulum or hairspring balance wheel). 

Weights are used as a driving power in large clocks, springs 
in small clocks and watches. The advantage of the latter lies 
in the fact that they occupy so little space. 

The escapement to which the pendulum or hairspring is attached 
regulates the rate at which the wheels revolve. This is accom- 
plished by allowing a cog of the escape wheel to pass with each 
swing of the pendulum or by the winding or unwinding of the 
hairspring. 

1. How may the speed of a pendulum clock be regulated? 

2. How can you regulate the speed of the balance wheel of 
your watch? 



THE CLOCK 




10 LABORATORY PROJECTS IN PHYSICS 

3. Suggest a method for determining how long this clock will 
run with one winding. Suggestion How many links are used 
up in one revolution of the large hand of the clock? 

4. What is the purpose of the pendulum? See Hoadley, or 
Millikan, Gale and Pyle. 

5. Does the minute-hand shaft run the hour hand or does the 
hour-hand shaft run the minute hand? 

6. Explain by means of the cog teeth why the minute hand 
goes twelve times as fast as the hour hand. 

Since the rate of vibration of a pendulum varies with its length, 
some means must be provided for correcting the effect of changes 
in temperature, contraction, and expansion. For instance, if a 
clock keeps accurate time at 70, it would run fast at 50 (pendu- 
lum shorter) and slow at 90. 

7. What is a compensated pendulum? See Millikan, Gale and 
Pyle, or Black and Davis, or Carhart and Chute. 

8. How is mercury used in the operation of one type of com- 
pensated pendulum? See Black and Davis. 

Another form of compensated pendulum depends upon the un- 
equal expansion of rods of different metals. In the balance wheel 
of a watch, compensation for changes in temperature is accomplished 
by a very thin strip of brass screwed to a strip of steel on the rim 
of the balance wheel. See Millikan, Gale and Pyle. 

BOOKS FOR SPECIAL STUDY: 

The Modern Clock Goodrich. 
Physics Millikan, Gale and Pyle. 



MEASURING LIQUID PRESSURES 



II 



5. MEASURING LIQUID 
PRESSURES 

To determine the specific 
gravity of mercury and 
to study liquid pressures 
by comparing the lengths 
of a mercury column and 
the water column which 
it balances in a manom- 
eter tube. 

MATERIALS. Manometer 
tube containing about three inches 
of mercury in each side; funnel; 
rubber connections ; mercury, me- 
ter stick ; two-foot glass tube. 

Place the manometer in a 
perpendicular position. 
(Caution. Handle carefully 
to avoid spilling the mercury.) 
By means of a funnel and a 
rubber connection pour water 
slowly from a beaker into 
one side till the surface of 
one mercury column stands 
exactly one inch above the 
surface of. the other. If the 
water does not go down on / 
account of air bubbles, push f= = 

a small wire up and down in FIG. 5. Open manometer or U-tube for de- 

, i , T_ -- / 11 terminine the specific gravity of mercury 

the tube. Measure Carefully and the g pr essure per Sjuare inch at the 

in inches the length of the bottom of a water column. 

water column supporting or balancing this one inch of mercury. 
With a rubber connection attach an additional two-foot length 



- ---Water 



Mercury 



12 LABORATORY PROJECTS IN PHYSICS 

of glass tubing to the water column side. Support it with a ring 
stand. Find the vertical lengths of water column required to 
support one and one half inches of mercury and two inches of 
mercury. 

1. Tabulate the results of your measurements in columns 
as follows : length of water column, length of mercury column, 
length of water column divided by length of mercury column. 

2. According to your measurements, how does the weight of a 
cubic inch of mercury compare with the weight of a cubic inch 
of water? (Specific gravity of a substance is the ratio of its 
weight to the weight of an equal volume of water.) 

3. According to your measurements, how many cubic inches 
of water would be required to balance a cubic inch of mercury? 

4. What is the specific gravity of mercury by accurate deter- 
mination? Density in grams per cubic centimeter, in the metric 
system, is the same as specific gravity in the English system. See 
Black and Davis, Figure 58, or Mann and Twiss, Pressure and 
Density, or Millikan, Gale and Pyle. 

5. When the extended water tube is inclined or slanted away 
from the perpendicular, how is the pressure on the mercury af- 
fected? 

6. If the tube is inclined, how should the height of water 
column be measured? Explain. 

7. A cubic foot of water weighs approximately sixty- two 
and one half pounds. Find the weight of a cubic inch of water. 
Find the weight in pounds of twelve cubic inches or a column one 
foot high and one square inch in cross section. The weight of a 
cubic inch of water is the same as the pressure per square inch of 
any water column one inch high. The weight of twelve cubic 
inches is the same as the pressure per square inch of any water 
column one foot high. 

8. What pressure per square inch is exerted at the bottom of a 
water column fifty feet high? 



MEASURING LIQUID PRESSURES 13 

9. With the specific gravity of mercury known, determine 
what pressure per square inch is represented by a column of 
mercury thirty inches high? Atmospheric pressure will support 
a column of mercury thirty inches high in a barometer. 

10. Does the thickness or shape of the tube have any influence 
upon the pressure per square inch at the bottom of a liquid? 
Explain. 

11. For any given liquid, upon what one condition does the 
pressure per square inch depend ? 

A water column two and three -tenths feet high exerts a pressure 
of one pound per square inch. For rough calculations a water 
column two feet high presses approximately one pound per square 
inch and a mercury column two inches high presses approximately 
one pound per square inch. 

BOOKS FOR SPECIAL STUDY: 

General Science Barber. 

Practical Talks on Farm Engineering Clarkson. 

Home Water Works Lynde. 

Submarines Talbot. 



LABORATORY PROJECTS IN PHYSICS 



6. MEASURING GAS PRESSURES 

To determine the pressure of gas in the illuminating gas pipe. 
MATERIALS. Manometer tube ; rubber connections ; glass jar ; glass tube. 

NOTE : If the manometer tube contains mercury from the previous experi- 
ment, ask the instructor to remove it. Fill the manometer half full of water, 
attach it to the gas outlet and open the gas cock. Measure the difference be- 
tween the levels on the two sides of the U-tube. 




FIG. 6. Measuring gas pressure with water in the manometer. 

1. What is the pressure of the gas in inches of water column? 

2. Calculate from No. i the pressure of the gas in pounds 



I 



MEASURING GAS PRESSURES 1 5 

per square inch. Refer to Experiment 5, Measuring Fluid Pres- 
sures. 

3. The common electric vacuum cleaners (centrifugal fan type) 
produce " suction " sufficient to support a column of water from 
eight to twelve inches in height. What pressure in pounds per 
square inch is produced by ten inches of water column ? 

4. The pressure of the air in an automobile tire is eighty pounds 
per square inch. How high would this pressure support a mer- 
cury column? a water column? 

5. If a water faucet pressure can support forty inches of mer- 
cury, what pressure is this in pounds per square inch? 

6. A man's blood pressure in the arteries is sufficient to sup- 
port a column of mercury five inches high. What pressure in 
pounds per square inch does this represent ? 

7. Attach a rubber tube to an eight-inch glass tube and connect 
the rubber end to the gas outlet. Insert the glass tube at least 
six inches under the surface of a jar of water. Turn on the gas 
and explain how this may be used to determine the gas pressure 
in pounds per square inch. 

8. If the atmosphere can exert sufficient pressure to hold up a 
thirty-inch column of mercury, what pressure is this in pounds 
per square inch? 

9. If a boy blows into a long glass U-tube with sufficient force 
to support a six-foot water column, what is his lung pressure in 
pounds per square inch ? 

BOOKS FOR SPECIAL STUDY: 

General Science Barber. 
General Science Hodgdon. 
Physics Mann and Twiss. 
Physics Black and Davis. 



i6 



LABORATORY PROJECTS IN PHYSICS 



7. THE HYDRAULIC ELEVATOR 
To construct a hydraulic elevator and study its operation. 

MATERIALS. Brass piston rod used in pump experiment ; No. 7 two-hole 
stopper (one hole at the center) ; No. 6 one-hole stopper ; No. 10 one-hole 
stopper ; four glass Ls ; two four- inch rubber tubes ; 
one twelve-inch rubber tube with faucet stopper. 

In the operation of hydraulic elevators 
the lifting force is obtained by allowing 
water under high pres- 
sure to enter one end 
of a cylinder contain- 
ing a movable piston. 
In the type of elevator 
illustrated here the piston is 
forced upward by the pressure 
of the water as it is directed 
into the lower end of the 
cylinder. When the piston 
reaches the top, the operator 
in the car, by means of a lever 
and cables, closes the inlet 
pipe A and turns a three-way 
valve. See Millikan, Gale and 
Pyle. Then, as the weight of the 
car pushes the piston down, the 
water in the cylinder passes out. 

Construct the apparatus as shown 
in the illustration. Note how the 
chimney is held. Do not clamp 
the glass. The piston rod and pis- 

FiG. 7. -The hydraulic elevator. ton stopper should fit Sufficiently 

tight to prevent leakage, but the piston should not move with too 
much difficulty. If the piston rod is too tight, place a few drops 




THE HYDRAULIC ELEVATOR 17 

of oil on it to reduce friction. To prevent a blowout at the wrong 
place, tie all rubber connections except the one at A with heavy 
thread. The one not tied will blow out in case of excessive pres- 
sure. Set the apparatus in the sink. If it does not work, try 
to correct the trouble. Ask the instructor for assistance if you do 
not succeed. 

1. If the area of the piston were one hundred square inches 
and the pressure of the water fifty pounds per square inch, what 
force in pounds would be exerted against the piston ? 

2. Make two diagrams of a three-way valve one showing the 
course of the water as the piston goes up and one as the piston 
goes down. See Millikan, Gale and Pyle. 

3. The piston which operates a large hydraulic elevator has an 
area of 200 square inches. If the water enters the cylinder at one 
hundred pounds per square inch, how much force in pounds does 
this piston exert ? 

4. How much work in foot pounds does this piston accomplish 
when the force obtained in problem 3 is pushed through sixty feet 
in lifting a car ? 

5. When the piston is going upward, in what direction is the 
pressure on the bottom stopper of the cylinder? State Pascal's 
Principle. Refer to texts. This principle is employed in the 
operation of hydraulic presses. See textbooks. If the piston is 
made large and the water is pumped into the cylinder at high 
pressure, the piston may be made to exert thousands of tons 
pressure. Hydraulic presses are used for compressing cotton, for 
making cider, for bending steel railroad rails, and for shaping 
metal parts known as pressed steel. 

6. Make a careful diagram of the apparatus. 

BOOKS FOR SPECIAL STUDY: 

Physics Millikan, Gale and Pyle. 
Physics Black and Davis, 
c 



i8 



LABORATORY PROJECTS IN PHYSICS 




8. FLOATING BODIES 

To show that a floating body displaces a volume of water equal 
to its own weight. 

MATERIALS. Lamp chimney ; No. 7 stopper ; lead weight ; aluminum pan 
6 in. top diameter ; platform balances ; hydrometer jar, 12 in. high, outside 
diameter 2! in. 

Balance the scales carefully 
before weighing any object. 
Make up a float according to 
the diagram, using a lamp chim- 
ney, a solid stopper (or one-hole 
stopper closed with a solid glass 
rod) and a lead weight. Weigh 
separately the float and the pan 
to tenths of a gram. 

Place the jar in the pan and 
carefully fill the jar with water 
to the point of overflowing. 
Gradually lower a weighted 
chimney till it is supported by 
the upthrust of the water. The 
water which is displaced by the 
float (chimney) will be caught 
in the pan. (NOTE : The relia- 
bility of the calculation and re- 
su lts will depend upon the accu- 
racy of your work.) Remove the 
FIG. 8. -A floating body displaces its own jar and reweigh the pan with 
weight of water. t h e overflow water in it. 

1. What is the weight of the float? 

2. What is the weight of the water which it displaces when it 
floats? 



FLOATING BODIES 19 

3. State the Law of Floating Bodies (Archimedes' Principle), 
Explain its application to the experiment just completed. Ex- 
plain any error which you may have found. See texts. 

4. Who was Archimedes? See Millikan, Gale and Pyle, or 
other text. 

5. When a boat or other object floats on water what two 
things are of equal weight ? 

6. With respect to the Law of Floating Bodies, when may a 
boat be expected to sink ? 

7. If a balloon goes up, what may be said of its own weight 
with respect to the air that it displaces ? A balloon is buoyed up 
by the air according to the law of floating bodies. A balloon rises 
from the earth through the air in a manner similar to that of a 
cork which has been pushed to the bottom of a jar of water and 
then released. 

8. If a -balloon falls to the ground, what may be said of its 
weight with respect to the air that it displaces? 

9. If a balloon just floats (stands still in the air), what may 
be said of its weight with respect to the air that it displaces? 

10. With respect to the Law of Floating Bodies, to what height 
may a balloon be expected to rise? 

11. Explain why a soap bubble filled with hydrogen goes up, 
while an ordinary air soap-bubble goes down. 

BOOKS FOR SPECIAL STUDY: 
Submarines Talbot. 
All About Ships Darling. 
Physics Millikan and Gale. 
General Science Barber. 
Household Physics Butler. 



20 



LABORATORY PROJECTS IN PHYSICS 



9. THE HYDROMETER 

To make a constant immersion hydrometer and test the specific 
gravity of a salt solution. 

MATEPJALS. Thin wall glass tube, length 3 in., outside diameter 7 mm., 
thickness of wall \ mm.; test tube, length 6 in., diameter f in.; platform 
balances ; No. 2 stopper ; lead shot ; salt solution. 

Specific gravity is the ratio of the weight of a 
volume of a substance to the weight of an equal 
volume of water. 



A. Making a Hydrometer. Insert a thin glass 
tube three inches in length into the stopper and, 
after placing a little crumpled paper in the bottom 
of a test tube, fasten the stopper firmly into it. 
Do not change the position of the stopper till the 
experiment is completed. Drop shot through 
the tube into the bottom of the test tube till the 
hydrometer sinks in fresh water beneath the 
stopper, to some convenient point on the thin 
glass tube. Mark this point with a loop of thread. 
See model made by the instructor. 

1. Balance the scales carefully before weigh- 
ing any object. Dry the hydrometer before weigh- 
ing. Weigh the hydrometer to tenths of a gram. 

2. Now float the hydrometer in the salt solu- 
tion of unknown specific gravity. Add enough 
shot to sink it to the former mark. Reweigh. 

/^ :-:--- ".-.".-. -vrh 3. How do these two weights give a basis for de- 
FIG. 9. Hydrometer termining the specific gravity of the salt solution? 
- constant immer- What is the specific gravity of the salt 

sion type. 

solution ? 

In the metric system a cubic centimeter of water weighs one 
gram. Therefore, the weight in grams of a cubic centimeter of 



THE HYDROMETER 



21 



any substance is the same as its specific gravity. A cubic centi- 
meter of mercury weighs 13.6 grams, therefore, its specific gravity 
is 13.6. Density, when expressed in grams per cubic centimeter, 
means the same as specific gravity. In general density refers to 
the weight of a unit volume of any substance, for example, grams 
per cubic centimeter or pounds per cubic foot. 

B. Hydrometers. The device constructed in A is a hydrom- 
eter of constant immersion and variable weight. Ordinary 
specific gravity hydrometers are of variable immersion and con- 
stant weight. The point to which the hydrometer sinks in water 
is represented as Specific Gravity i. In a lighter liquid like al- 
qohol, sp. gr. 0.8, the hydrometer sinks deeper to a point marked 0.8. 
In a heavier liquid like glycerine the hydrometer sinks less deeply 
to a point marked 1.26. In a lead storage battery, such as is used 
in automobile self-starting and ignition systems, a specific gravity 
below 1.15 indicates that the battery is completely run down and 
needs recharging. A battery fully charged tests approximately 
sp. gr. 1.3. 

5. How could the hydrometer of A be made to indicate specific 
gravity directly like the ordinary specific gravity hydrometer? 

6. Make a careful diagram of a typical hydrometer (variable 
immersion) and explain it. See Hoadley, Black and Davis, Mil- 
likan, Gale and Pyle. 

The Baume hydrometer was one of the earliest hydrometers 
in use and its scale does not refer directly to the weight of an equal 
volume of water. The ordinary specific gravity hydrometers 
compare the weight of a substance with the weight of an equal 
volume of water. Similar instruments used for various commer- 
cial purposes are alcoholometers for liquors, salimeters for salts, 
lactometers for milk, etc. 
BOOKS FOR SPECIAL STUDY: 

General Science Barber. 

Physics Black and Davis. 

The Gasoline Automobile Hobbes, Elliott and Consoliver. 



22 



LABORATORY PROJECTS IN PHYSICS 



10. THE SIPHON 
To operate a siphon and explain its action. 



MATERIALS. 

tube. 



Two 24-in. glass tubes; two 12 oz. bottles; zo-in. rubber 




Fill the bottles half full of 
water. Connect the glass 
tubes by means of the rubber 
tube and fill with water. 
Close the tube by pressing at 
the rubber connection and in- 
sert one end in each bottle. 
Note that if one bottle is 
raised so that the water level 
is higher in one than in the 
other, water flows through 
the tube until the levels are 
the same. 

1. When a siphon is in 
operation, which arm con- 
tains the heavier water 
column? 

2. When the water level 
in the two bottles is the 
same, why does the water 
column not separate at the 
top and run back into the 
bottles? Refer to texts 
Siphon. 

3. How could you make a 
siphon work more rapidly? 

4. Is it possible to siphon water from a lower level to a higher 
level ? Explain. 



I 







I 


j 


k 


:i%i^ 


- r--zrf~ 


"Zrll 


: :3 1] 


--'- 


- -T- 


^ ~ 


: ^=" 



FIG. 10. A siphon. 



THE SIPHON 23 

5. If we should make a siphon reaching over a house forty feet 
high, would you expect water to remain at the top of the pipe? 
Explain. See Millikan, Gale and Pyle, or other texts. 

6. When the siphon is working, if a hole were made in it at the 
top, what would be the result ? Explain. 

7. Mention at least two uses for the siphon. See Carhart and 
Chute, or other texts. 

Suggestions. The pressure of the atmosphere (15 Ib. per sq. in.) 
is exerted upward against both ends (water levels of the siphon). 
Thus, so far as the atmospheric pressure is concerned, the two 
pressures are opposite and they balance each other. But the 
weight of the water in the long arm decreases the upward pressure 
of the atmosphere on the long arm side, and the weight of water in 
the short arm decreases the upward pressure of the atmosphere 
less than on the long arm side. Therefore, the greater force on the 
short arm forces water up the short arm. The explanation may be 
stated in other words as follows : 

On account of its weight, the water in the two arms of the 
siphon tends to separate at the top and produce a vacuum, but 
atmospheric pressure prevents this. The weight of the water on 
the long arm side produces a greater suction (tendency to form 
a vacuum at the top), than on the short arm side, therefore, water 
flows from the short arm side into the long arm side. 

If a siphon more than 34 feet high should be filled with water, 
the water would separate at the top and form a vacuum because 
the atmospheric pressure (15 Ib. per sq. in.) can support only a 
34-foot column. The water in both arms would drop back to 
the 34-foot level. This siphon, of course, would not flow. 

BOOKS FOR SPECIAL STUDY: 

General Science Barber. 
Household Physics Butler. 
Mechanics of the Household Keene. 



LABORATORY PROJECTS IN PHYSICS 



ii. THE SIPHON FOUNTAIN 
To construct a siphon fountain. 



DO 




FIG ii. The siphon fountain. 



MATERIALS. 1 2-oz. bottle ; No. 7 two- 
hole stopper; 5-in. nozzle tube; 3-in. glass 
tube; two i2-in. rubber tubes; two i2-oz. 
bottles ; 2-f t. glass tube. 

Support the bottle on a ring stand 
by means of rings. See instructor's 
model. Insert a glass nozzle tube 
through a two-hole stopper into the 
mouth of the inverted bottle. Con- 
nect the end of this tube to a jar of 
water on the table. Through the 
other hole of the stopper lead a tube 
to a jar on the floor. Fill the tube 
leading to the floor with water and 
insert into the jar on the floor. See 
model made by the instructor. 

1. Explain the condition of the air 
in the bottle when the fountain is 
in operation. 

2. How could the fountain be made 
more forceful? 

3. Assuming the atmospheric pres- 
sure to be 15 Ibs. per sq. in., how 
much does a three-foot column lead- 
ing to the floor decrease the pres- 
sure of the air in the bottle? What 
is the pressure of the air in the 
bottle when a three-foot tube is at- 
tached? 



PRESSURE TANK WATER SUPPLY BOYLE'S LAW 25 

4. What would be the approximate pressure of air in the bottle 
if the water column leading from it were 20 feet long? 

5. Kerosene is four-fifths as heavy as water. If water can be 
siphoned 34 feet, how high can this oil be siphoned? 

6. How high can mercury be siphoned? Mercury is 13.6 
times as heavy as water. 

7. State the conditions that must be fulfilled in the operation 
of a siphon. 

BOOKS FOR SPECIAL STUDY: 

General Science Barber. 
Household Physics Butler. 
Physics Carhart and Chute. 

12. PRESSURE TANK WATER SUPPLY 
BOYLE'S LAW 

To illustrate the operation of a pressure-tank water supply for 
a dwelling house. 

MATERIALS. Large glass tube, 2 feet long, outside diameter three-quarters 
inch, inside diameter nine-sixteenths inch; glass tube 2 feet long; heavy 
rubber tubing, two twelve-inch pieces; brass T-tube; No. o one-hole rubber 
stopper; small bilge pump; hydrometer jar; two strong screw clamps; 
heavy thread ; half meter stick. 

In country districts isolated from the regular city water mains, 
buildings are sometimes supplied with water under pressure by 
pumping the water from a well with a gasoline engine, windmill, 
or some other source of power, into a large heavy metal tank, 
located in the basement. The principle involves having the upper 
part of the tank filled with air. Water is forced into the lower 
part of the tank by means of a pump and the air above is compressd. 
The compressed air then acts with continuous pressure to force 
the water into the pipe leading to the faucets in the building. 

The compressed air in the tank acts according to Boyle's law. 
The volume of an enclosed gas varies inversely as the pressure on it. 



26 



LABORATORY PROJECTS IN PHYSICS 



This means that by doubling the pressure on a volume of air, or 
other gas, its volume is reduced one-half. See text. 



jFfepresents pressure 
tank /ocated tn basement 
of a dwe///n<p house. 



SP 



Ftepresents__ _ 
water p/pe 
/eac//no; to 
upper floors. 




Pump 

operated either 

by hand by 

e/ectr/c/ty, 

yas engine or 

wincf-m/ff. 



FIG. 12. Compressing a gas (air), Boyle's Law. 

NOTE. , To avoid spilling water on the laboratory tables and 
floor, place the apparatus in the laboratory sink. 

( Tie all rubber tube connections with thread to prevent blowing out.) 
Place about six inches of water in the large tube. Insert stopper 
tight and pressure inside at the beginning should be atmospheric 
(15 Ibs. per sq. in.). Close clamp B and slowly pump in additional 






PRESSURE TANK WATER SUPPLY BOYLE'S LAW 27 

water until the water level is forced upward about one-fourth of 
the distance to the top. The enclosed air is then reduced to 
about three-fourths of its original volume. Then close the clamp 
at A to hold the pressure. At this point measure carefully in 
millimeters the length of the compressed air column. Now re- 
lease clamp B and allow the compressed air to force the water 
out through the thin tube. When the enclosed air is again at 
normal atmospheric pressure, measure in millimeters the length of 
the air column. The length of the air column of a uniform tube 
may be taken to represent its volume. 

1. Under what pressure is normal atmospheric air? See text. 

2. What was the length of the enclosed gas column (air) under 
atmospheric pressure (the second measurement) ? 

3. What was the length of the enclosed gas column under added 
water pressure (first measurement) ? 

4. According to Boyle's Law, calculate the total pressure on the 
inclosed air when the volume was reduced. The pressure will be 
as many times the atmospheric pressure (15 Ibs.) as the volume 
(when compressed) is less than the atmospheric volume (normal 
volume). 

5. What does the total pressure of question 4, minus 15 Ibs., 
represent ? 

6. If the volume of atmospheric air is compressed to one- third 
of its normal volume, what total pressure per square inch (includ- 
ing atmospheric) would then be exerted upon it ? 

7. If the total pressure in a pressure tank in a house is thirty 
pounds per square inch (15 Ibs. above atmospheric) how high 
would this pressure raise water in the pipes of the building? See 
illustration, Barber's General Science Pneumatic Tank. 

BOOKS FOR SPECIAL STUDY: 

Mechanics of the Household Keene. 
General Science Barber. 
Home Water Works Lynde. 



28 



LABORATORY PROJECTS IN PHYSICS 



13. FAUCET WATER PRESSURE BOYLE'S LAW 
To measure faucet pressure with the closed manometer. 

MATERIALS. Same apparatus as in the Pressure Tank Water System 
with glass L-tube in place of T-tube ; pressure-tubing and faucet stopper. 

Fill the glass tube 
half full of water and 
attach it to the ring 
stand as shown in 
the illustration. By 
means of tubing and 
a rubber stopper, 
connect it firmly to 
the faucet. Note 
that the air enclosed 
in the tube is com- 
pressed when the 
water from the fau- 
cet rushes in. (Cau- 
tion. If the faucet 
pressure is very high, 
it will be necessary 
to use special pressure 
tubing and special 
precautions will be 
required to prevent a 
blow-out.) Measure 
in millimeters the 
length of the enclosed air column with faucet turned on and the 
air compressed. Remove the faucet stopper, allowing the com- 
pressed air to expand again to normal volume. Measure again 
at normal volume, holding the stopper (water level in the stopper) 




FIG 



13- Faucet water pressure measured by compress- 
ing air in a tube Boyle's Law. 



FAUCET WATER PRESSURE BOYLE'S LAW 29 

on the level of the water in the compression- tube. If the pressure 
volume is measured first any air bubbles which enter with the 
pressure water will not cause an error in the result. 

1. If this final volume represents atmospheric pressure (15 Ibs.), 
what pressure in pounds per square inch is represented by the 
volume when the faucet pressure is on? Apply Boyle's Law. 
This pressure includes both atmospheric pressure and the addi- 
tional pressure of the water. Subtract fifteen pounds from this 
pressure to get the pressure of the water alone. 

2. Normal air is under a pressure of fifteen pounds per square 
inch. If a faucet pressure compresses the air to one-fifth of its 
normal volume, what total pressure produces this effect? 

3. In question 2 how much of the pressure is caused by the 
water in the pipes and how much by atmospheric pressure ? The 
atmospheric pressure is on the water at the reservoir or where it 
enters the pipes. 

4. In question 2 how many feet of water column must be added 
to the fifteen pounds atmospheric pressure to produce the total 
pressure? Two and three-tenths feet of water column produce 
one pound pressure per square inch. 

To determine the pressure due to water alone, substract fifteen 
pounds from the total pressure of question 2. This is the pres- 
sure of the water as indicated by an ordinary pressure gauge. 

5. If the air in an automobile tire is compressed to one-fifth 
of its normal volume, what pressure per square inch does it exert 
against the inside of the tire? 

6. What pressure is exerted against the outside of an automo- 
bile tire? 

7. If a pumped up automobile tire were placed in a vacuum, 
would it be more or less likely to burst? Why? 

BOOKS FOR SPECIAL STUDY: 

Practical Physics Black and Davis. 
Household Physics Butler. 
Mechanics of the Household Keene. 



30 LABORATORY PROJECTS IN PHYSICS 

14. STEAM HEATING SYSTEM 

To construct a one-pipe steam heating system. 

MATERIALS. Bunsen burner ; 500 c.c. flask with neck for No. 6 stopper ; 
two 12-oz. bottles; two brass T-tubes; one glass L-tube; glass tube 4 inches 
long ; glass tube 1 2 inches long ; 2 glass tubes 8 inches long ; No. 6 two-hole 
rubber stopper ; two No. 7 2-hole rubber stoppers ; two rubber tubes, 5 inches ; 
wire gauze ; pinch clamp ; three short rubber tubes. 



Ji&d/ator 



DO 
DO 



J?ad/ator\ 



Water _ 

t. -^ 

Slope 



130 
DO 




A. 



FIG. 14. One-pipe steam heating system. 

Constructing a Steam Heating System. Set up the appara- 



tus as shown in illustration. Observe, carefully, the proper slop- 
ing of pipes for drainage. Boil water in the flask, having outlets 
of both bottles open. When the bottle nearer the flask becomes 
heated, close the pinch clamp. 



STEAM HEATING SYSTEM 31 

1. How could the pressure in these bottles and in the entire 
system be increased? In steam heating systems, a pressure of 
from o to 5 Ibs. per square inch is common. However, in small 
dwellings the pressure is frequently allowed to drop to % Ib. or less, 
except on very cold days. In these systems, all air-escape valves 
of radiators, corresponding to pinch clamps, should be closed 
during regular operation. If the pressure rises too high, an auto- 
matic safety valve at the boiler allows the steam to blow off into 
the basement. 

2. After the water reaches the boiling point (212 F.), what 
becomes of all the heat that goes from the flame into the flask, 
since the temperature of the water is not raised above 212 F.? 

3/ How does increasing the pressure affect the boiling point? 
See Millikan, Gale and Pyle, Black and Davis, Ontario Physics. 
In ordinary steam heating systems, a fairly constant temperature is 
maintained in the radiators, the room temperature being regulated 
best by having two or more radiators in each room. This is 
desirable, because one-pipe steam radiators must be operated with 
the valve completely open or they must be turned off completely. 

4. How is it possible to provide for three different rates of 
heating a room by means of two radiators, a small one and a large 
one? This provides for temperature conditions at different sea- 
sons. In hot-water systems the room temperature may be regu- 
lated by varying the temperature of the water or by opening the 
radiator valve more or less widely. 

5. Explain what is happening in the steam radiator. One gram 
of steam in condensing to water gives out 540 calories of heat. 
A radiator is considered efficient if under the ordinary conditions 
of steam pressure, volume and temperature of surrounding air, 
it will condense a large amount of steam in a given time. Con- 
sequently the amount of heat given off depends upon the differ- 
ence of temperature between the steam in the radiator and the 
surrounding air, the velocity of air over the radiator, and the 
color of the radiator. If a radiator is black, it gives off a little 



32 LABORATORY PROJECTS IN PHYSICS 

more heat than one painted some lighter color. Open pipe-coils 
allow air to circulate more freely and, therefore, give off more 
heat than radiators. 

6. What is the advantage of the large feed circuit (basement 
circuit from the boiler back again to the boiler) in a one-pipe 
system? (A 2 or 2^ inch basement circuit pipe is common in 
dwellings.) Two-pipe systems may have smaller pipes. 

7. Why is it necessary to have a continuous down slope from the 
radiators to the boiler? What would happen if a pocket (imper- 
fect drainage) occurred in the pipe leading steam from the boiler 
to the radiators? 

8. What is the purpose of a small valve (air vent) on the side of a 
steam radiator? See Mechanics of the Household, Keene Vents. 

B. Vacuum Steam Systems. Dwelling house vacuum systems 
have special valves which prevent air from entering the radiators 
when the steam pressure drops. A vacuum steam system, if it 
works properly, is economical in moderate weather because it re- 
quires less heat to force vapor into the radiators and thus saves 
coal. In dwelling houses these special systems are hard to keep 
air-tight and often work no better than ordinary steam systems. 

Special vacuum systems are used in large buildings, operated 
by means of a special suction pump, to which pipes lead from 
the radiators. This pump keeps the radiators free of air and 
prevents bumping when the valves are partially closed. See 
General Science, Barber. 

C. Noises. Explain noises (a) when steam enters a cold radia- 
tor (expansion of the metal parts), (b) when the inlet valve is only 
partially open (bumping of water and vacuum hammer). 

BOOKS FOR SPECIAL STUDY: 

Household Physics Butler. 
Physics of the Household Lynde. 
Mechanics of the Household Keene. 
General Science Barber. 



HEAT OF CONDENSATION LATENT HEAT 



33 



15. HEAT OF CONDENSATION (OR VAPORIZATION) 
LATENT HEAT 

To find how many heat units (calories) are given out by the 
condensation of a gram of steam 

MATERIALS. Bunsen burner ; two 500 c.c. flasks ; L-tube with long arm 
8 inches long ; No. 6 stopper ; balances ; Centigrade thermometer ; wire gauze ; 
cloth or paper insulator. 

A . Determining the Heat of Vaporization. 
Construct a steam generator by means of 
a flask, a stopper, and a delivery tube as 
shown in instructor's model. Fill the flask 
half full of water and heat it till it boils with 
Bunsen burner flame so that a strong jet of 
steam flows from the delivery tube. 

NOTE. The success of this experiment 
depends chiefly upon accurate weighing 
and reading of the temperatures. Bal- 
ance scales before weighing. 



_ Cent/grade 
thermometer 





of water 



F T G. 15. Steam generator and apparatus for determining the amount of 
heat given out when a gram of steam condenses to water. 

Weigh the second flask empty, and then add very carefully 400 
grams of cold water. Place a centigrade thermometer in this flask 
and note the starting temperature of the water. Insulate the flask 



34 LABORATORY PROJECTS IN PHYSICS 

with a wrapping of paper. Holding the weighed flask with the 
hand, place it quickly into position so that the steam is delivered 
into the center of the volume of water. The cold water will con- 
dense the incoming steam and the temperature of the original water 
will rapidly rise. (Caution. Do not at any time during this opera- 
tion remove the flame from the steam generator flask, as this would 
cause a partial vacuum.) Keep the thermometer in the flask 
during the operation, stir slowly, and when the temperature has been 
raised approximately 20 degrees, quickly remove the flask from 
the steam generator, and note accurately the temperature reading 
on the thermometer. Reweigh and find how many grams of steam 
were condensed. 

1. What was the starting temperature? 

2. What was the final temperature ? 

3. How much steam in grams was condensed to water? 

4. How many calories of heat were required to bring the 
original water to its final temperature (grams water X degrees 
rise) ? A calorie is the amount of heat required to raise a gram 
of water one degree centigrade. The grams of steam, after it was 
condensed, must also have cooled from the boiling point to the 
final temperature and, therefore, must have given up some heat 
to the original water (grams steam X drop in temperature from 
100 degrees to the final temperature). Subtract these calories 
from the total heat given to the original water, because we wish 
to know only the heat given out by the condensing process, not 
by the further cooling after condensing. Repeat the experiment a 
second time as a check. 

5. How many calories of heat were given out by the con- 
densing process only (according to your calculation)? 

6. How many calories of heat were given out by one gram of 
condensing steam (on the basis of your calculation)? 

7. How do your results compare with the accurate determina- 
tion of the Heat of Vaporization of Water? Refer to text. In- 
quire of instructor whether your results are satisfactory. 



HEAT OF CONDENSATION LATENT HEAT 35 

8. If some heat were lost by condensation of steam in the 
delivery tube, would this make your result lower or higher than 
it should be? 

9. If some heat were lost through the flask to your hand, or 
to the surrounding air, would this make your result lower or 
higher than it should be ? 

10. If some heat were lost in heating the glass of the condensing 
flask, how would this affect the result ? 

11. How is this experiment related to the heat which comes 
from a steam radiator? 

12. Explain the fact that evaporating moisture, perspiration, 
or a few drops of alcohol, or ether, on the hand produce a 
cooling effect. 

13. Is it possible to raise the temperature of water boiling in an 
open kettle above 212 F. ? Explain. 

14. It takes less than one-fifth as long to heat a quantity of 
ice water to the boiling point as it takes to change it completely 
from boiling water into steam. Explain this statement. 

A common method of making artificial ice depends upon the 
heat of vaporization of liquid ammonia. When liquid ammonia is 
vaporized it takes in so much heat that, if water stands near, the 
heat is taken away from the water and it freezes. 

B. Law of Vaporization. The general law relating to vapori- 
zation and condensation may be stated as follows : When a liquid 
changes to a gas, it takes in heat or it must get heat. Con- 
versely, when a gas changes to a liquid it gives out heat. 

BOOKS FOR SPECIAL STUDY: 
Heat Ogden. 
Physics Mann and Twiss. 
Practical Physics Black and Davis. 
Mechanics of the Household Keene. 
General Science Barber. 



LABORATORY PROJECTS IN PHYSICS 



16. HOT-WATER HEATING SYSTEM 

To construct a model of a hot-water heating system and study 

its operation. 

MATERIALS. Two i2-oz. bottles; 500 c.c. flask; three brass T-tubes ; 
two i2-in. glass tubes; three 6-in. glass tubes; funnel; rubber connections 
and tubing; two No. 7 3-hole rubber stoppers; No. 5 2-hole rubber stopper; 
wire gauze ; Bunsen burner ; pinch clamps. 



Rad/ator- 




: U -: Rad/ator 



A/r va/ve 



-A/r va/ve 



FIG. 16. Hot-water heating system. 



HOT-WATER HEATING SYSTEM 37 

A. Constructing a Hot-Water Heating System. Set up appara- 
tus as shown in the illustration. The expansion tank should stand 
at a higher level than the radiators. Fill the apparatus with water 
and heat the flask. Make all connections tight. Tie with heavy 
thread if necessary. Force stoppers in as tight as possible to 
avoid flooding the table. Note carefully the position of clamps 
and rings. 

The Operation. Put a flame under the flask. As the water in 
the boiler becomes heated, a circulation is set up. The water in 
a hot-water heating system should not be allowed to boil. 

1. What causes this circulation in a hot- water heating sys- 
tem? 

2. What is the reason for making one pipe reach to the bottom 
of the flask? 

3. Why does the circulation move more slowly when the 
radiators get hot than when they are cold? 

4. It takes longer to heat up a hot-water heating system than 
a steam system. Explain. 

5. What is meant by the specific heat of a substance? Refer 
to text for the meaning of specific heat. How is the specific heat 
of water involved in question four? Why is a hot-water heating 
system less variable in temperature than a steam heating system? 

6. What is the purpose of the expansion tank? See diagram 
General Science, Hodgdon ; Household Physics, Butler. 

7. Air collects in hot-water radiators. Where does it come 
from? 

8. Can you suggest a means by which you might cause the 
circulation to flow in the opposite direction? 

9. Radiators -that are directly over the furnace are usually 
warmer than those that are at the same level but in some more 
remote position. Explain. 

10. Draw a diagram of the apparatus and indicate the direction 
of flow by means of arrows. 



38 LABORATORY PROJECTS IN PHYSICS 

B. Heating Systems. There are three common types of house 
heating systems which include furnaces : a. Steam, b. Hot water. 
c. Hot air. 

Advantages of hot-water compared with steam in heating sys- 
tems, a. Little possibility of explosion, b. The amount of heat 
in the radiator may be controlled perfectly at the supply valve. 
c. Little or no noise, d. Hot-water radiators give off heat below 
the boiling temperature and, therefore, require less coal in moder- 
ate weather. 

Disadvantages of hot- water as compared with steam, a. Danger 
of freezing, b. Costs about one-third more to install, c. Radia- 
tors are larger and require more room space, d. Hot-water re- 
quires longer to heat up. 

BOOKS FOR SPECIAL STUDY: 

Household Physics Butler. 
Physics of the Household Lynde. 
General Science Barber. 
Mechanics of the Household Keene. 

17. HEAT OF FUSION (LATENT HEAT) 
To determine the heat required to melt one gram of ice. 

MATERIALS. Dry cracked ice or snow ; two 250 c.c. beakers; balance; 
centigrade thermometer ; wire gauze ; Bunsen burner. 

A. Determining the Heat of Fusion of Ice. Heat a beaker full 
of water to the boiling point (100 Centigrade). Balance scales 
before weighing. Weigh a second beaker empty. Fill quickly 
with dry snow or pieces of ice and re weigh, finding the weight of 
the ice. Slowly pour boiling water on the ice until it is melted, 
stirring constantly. Avoid a great excess of hot water. When 
the ice is melted record the temperature immediately and then 
reweigh. 

1 . What was the final temperature ? 

2. How many grams of boiling water were poured in? 



HEAT OF FUSION (LATENT HEAT) 



39 



3. How many calories of heat came from the boiling water 
(grams of boiling water X degree fall from 100 degrees to the 
final temperature) ? 

4. After the ice was melted, how many calories were needed 
to raise the ice water at o C. to the final temperature (grams of 
ice water X degrees rise from o C. to the final temperature) ? 

5. How many calories were used in the melting process only 
(difference between answers 3 and 4)? 

6. How many grams of ice did this heat 
melt? How many calories are required to 
melt one gram of ice (heat of fusion of ice) ? 
Inquire of instructor whether your results are 
satisfactory. 

7 . What are some sources of error in this 
operation? How does your result compare 
with the accurate determination of the heat 
of fusion of ice ? Refer to text. 

8. To what temperature would a gram of 



water 



auze 




Weighed /'ce- 




FIG. 17. Apparatus for determining the amount of heat required to melt a gram 

of ice. 



40 LABORATORY PROJECTS IN PHYSICS 

water at o C. be raised by the heat required merely to melt a 
gram of ice? 

9. How does the amount of heat required to raise a kettle full 
of ice at o C. to the boiling point compare with the heat required 
to raise an equal weight of water from o C. to the boiling point ? 

B. Conclusions. This experiment shows that when ice melts it 
must take in a definite quantity of heat. Strange as it may seem, 
it is also true that when ice is freezing it is losing heat. For ex- 
ample, a tub of water freezing in a cellar prevents the tempera- 
ture from falling much below the freezing point so long as the 
water is not all frozen. Freezing water keeps a room warmer than 
it otherwise would be. Apples and potatoes which freeze at some- 
what below the freezing point of water are sometimes protected in 
a cellar by having large vessels of freezing water near by. It is 
usually warmer in the vicinity of a freezing lake than at other points. 

Heat taken in when snow melts thus prevents a bed of snow 
on the ground from changing suddenly to water and serves as a 
protection against floods and sudden temperature changes in the 
atmosphere. 

10. Explain why the heat that gradually passes into a refrig- 
erator or ice box does not raise the temperature of the ice box. 
What becomes of any heat that gets in? 

11. Before placing a piece of ice in the refrigerator, why not 
wrap it in a blanket or in heavy paper to keep it from melting? 

C. Law of Fusion. The general law relating to freezing and 
melting may be stated as follows : When a solid changes to a liquid 
it takes in heat or it must get heat. Conversely when a liquid 
changes to a solid it loses or gives out heat. 

BOOKS FOR SPECIAL STUDY: 
Heat Ogden. 

Practical Physics Black and Davis. 
Physics Millikan, Gale and Pyle. 
Household Physics Butler. 



KITCHEN HOT-WATER TANK 



1 8. KITCHEN HOT-WATER TANK 

To construct a model of a kitchen hot-water heater and explain 

its action. 

MATERIALS. No. 50 Macbeth chimney; two i2-oz. bottles; two glass 
L-tubes; one L-tube with one 8-in. arm; brass T-tube; two i2-in. glass tubes; 
two i2-in. rubber tubes; two 
lo-in. glass tubes ; one 6-in. 
glass tube; No. 7 two-hole 

Source of__ 
tvafer suf>p/y 



rubber stopper ; No. 10 one- 
hole rubber stopper; wire 
gauze ; pinch clamp ; Bunsen 
burner. 



W/re 
gauze 




A. Constructing a 
Kitchen Tank Model. 

Construct the apparatus 
following instructor's 
model and fill with water. 
Heat slowly at lower end 
of side tube, with wire 
gauze above the burner. 
The burner placed at this 
point represents a 
kitchen range or 
gas heater con- 
nectedwithahot- 
water tank. 

1. What causes the 
water in the tank to be- 
come heated? Does the 
water move? Explain. 

2. When first apply- FIG. 1 8. Range-tank water-heater. 

ing heat, touch the pipe at different points and indicate the path 
of the heated water. Diagram the apparatus, showing the direction 
of flow by means of arrows, 



42 LABORATORY PROJECTS IN PHYSICS 

3. Does the hot water in the tank mix readily with the cold 
water ? Explain. 

4. Why is the hot water taken in at, or near, the top of the tank ? 
In a gas-heated water tank, the water passes from the bottom 

of the tank through the heating coil, and then to the top of the 
tank, from which point it leads directly to the faucets. See 
Household Physics, Butler. When water is heated by a coal 
range, it passes from the bottom of the tank to the " water-back " 
in the range, and thence to the top of the tank, or to some other 
point at the side of the tank. 

5. Why should the cold-water inlet be near the bottom of the 
tank? 

6. Would you expect the circulation to continue as rapidly after 
the tank gets hot? Why? 

7. Why should the pipes of a kitchen tank system be filled 
before they are made hot in the range ? What, might happen if 
cold water should rush into very hot pipes ? 

8. If the tank gets very hot, steam sometimes forms in the 
" water-back " or " water-front " causing loud noises. Explain. 

B. The Gas Water-Heater, Instantaneous. The kitchen tank 
above provides for storing a quantity of hot water which is heated 
slowly by the stove or by a gas heater, and flows to the tank by a 
convection current. Where gas is available, hot water in any 
quantity may be obtained instantaneously by direct heating of the 
coils of a large gas water-heater. By a water pressure mechanism 
these devices automatically turn on the gas when the hot-water 
faucet in the house is opened and turn it off when the faucet is closed. 

9. What are some advantages of an automatic instantaneous 
gas water-heater as compared with a kitchen range tank ? 

BOOKS FOR SPECIAL STUDY: 

Practical Physics Black and Davis. 
Household Physics Butler. 
Mechanics of the Household Keene. 



THE LIQUID CELL AND THE DRY CELL 



43 



19. THE LIQUID CELL AND THE DRY CELL 
To make a Leclanche cell and study its action. 

MATERIALS. Base block 5X5X2 in.; round battery-jar 5^ in. high 
X2f in. in diameter; ammonium chloride (sal ammoniac) ; zinc battery rod; 
carbon rod from an old dry battery cell ; Bunsen burner ; electric bell ; No. 24 
insulated wire; jar of 10 per cent nitric acid, to be used only by the instructor; 
cardboard, for separating battery rods at top ; short glass tube, for separating 
battery rods at bottom ; glass stirring rod. 



Card-board to keep 
rods separated 
at to/?. 




Carbon rod- 



FIG. 19. A liquid cell Leclanch6 type. 

A. Making a Liquid Cell. Make up an ammonium chloride 
solution by filling the battery jar one-fifth full of ammonium 
chloride salt and adding water till the top of the liquid stands 
one inch from the top of the jar. Dissolve by stirring with a 



44 LABORATORY PROJECTS IN PHYSICS 

glass rod. Stand the zinc rod in the solution at one side of the 
jar, and the carbon rod at the other. Use a short piece of glass 
tubing at the bottom of the jar and cardboard at the top to keep 
the electrodes separated. See instructor's model. 

1. Connect wires to the electrodes and ring an electric bell. 

2. Make a drawing of the cell indicating the materials used, and 
showing the direction in which the current flows. The current 
is considered as flowing from the positive to the negative electrode 
outside the solution. The negative electrode is the one acted 
upon more by the electrolyte. In this case the zinc is negative. 

3. In the operation of the Leclanche cell, what salt and what 
two gases are produced by the chemical reaction? See Carhart 
and Chute. 

B. Polarization. When this cell is attached to the electric bell, 
it rings the bell for a short time and gradually becomes exhausted. 
This phenomenon is due to polarization. Hydrogen molecules 
are set free as a result of the chemical action. The carbon elec- 
trode gradually becomes covered with a thin film of hydrogen, 
which prevents the flow of the current. Polarization may be 
counteracted by placing in contact with the carbon electrode 
some form of oxidizing agent, as, for example, manganese dioxide. 
The hydrogen reacts with the manganese dioxide, forming water. 
This cell may be temporarily depolarized by heating the carbon 
rod in a gas flame for three minutes. It may be depolarized more 
effectively by heating it for three minutes and holding it for about 
a minute, while hot, in a solution of ten per cent nitric acid. (NOTE. 
Nitric acid is a strong oxidizing agent. It is also a strong acid. 
It will discolor and destroy clothing.) Hold the carbon rod in a 
gas flame for about three minutes. The instructor will then 
depolarize it for you in nitric acid. 

4. What depolarizer or oxidizing agent is used in the con- 
struction of dry cells? See Carhart and Chute. 

5. What is the voltage of an ammonium chloride cell? The 



THE LIQUID CELL AND THE DRY CELL 45 

dry cell is a form of the ammonium chloride cell. Large cells 
have the same voltage as small ones. See Millikan, Gale and Pyle 
-Leclanche Cell. 

6. Connect your cell in series with the cell made by some 
other student. How many volts should two cells in series have? 
Four cells in series ? Refer to text. 

7. Operate an electric bell by means of two liquid cells in 
series. What evidence have you that the voltage of two cells is 
able to force more current through the resistance of the bell than 
one? 

8. Describe briefly the construction of a simple liquid cell 
which uses sulphuric acid as the electrolyte. Diagram it. Refer 
to some physics text. 

9. What is meant by local action? See textbooks. 

10. Diagram a dry cell. See Hoadley or Carhart and Chute. 

C. The Dry Cell. The dry cell is a modification of the Leclanche 
cell. The negative electrode is a zinc can containing a carbon rod 
at the center. Between the zinc and the carbon is packed a damp 
mixture of ammonium chloride, sand, manganese dioxide, etc. 
The manganese dioxide is a depolarizer. The top of the can is 
then sealed with pitch to prevent the so-called dry cell from really 
becoming dry. If the pitch is cracked, or if holes are made in the 
zinc so that the moisture dries out, the cell becomes useless. The 
voltage of a dry cell remains fairly constant whether it is new or 
nearly discharged. The amperage will vary widely, depending 
upon age and usage. When a dry cell is short-circuited, the 
stored-up energy produces heat in the wires and in the cell. At 
present the dry cell has largely replaced the older forms of liquid 
cells. 

BOOKS FOR SPECIAL STUDY: 
Physics Mann and Twiss. 
The Boy Electrician Morgan. 
Physics Millikan, Gale and Pyle. 



LABORATORY PROJECTS IN PHYSICS 



20. MEASURING ELECTRIC CURRENT 

To wire dry cells in series, and measure volts pressure and 

amperes flow. 

MATERIALS. Two dry cells ; No. 24 copper wire (insulated) ; battery- 
voltmeter ; thirty-five ampere battery ammeter ; push button. 




Battery ammeter- or- 
vo/tmeter-mounted 



Dry ce// 



FIG. 20. Wiring for measuring voltage or for testing amperage of a dry cell. See 
caution under B below regarding the use of expensive ammeters. 

A. Making Measurements. Attach two wires firmly to the 
binding posts of one of the cells, taking care that the two wires 
do not touch each other and cause a short circuit. (A short 
circuit would heat the wires and rapidly waste away the energy 
of the cell.) Attach one wire to one of the voltmeter binding 
posts. Connect the other wire to one side of the push button. 
From the other side of the push button connect a wire to the 
second post of the voltmeter. Now push the button and read the 
voltage of the dry cell. In the same way measure the voltage of 
the second cell. (Caution. In measuring amperes, the thirty-five 
ampere ammeter must be connected in series with a push button in 
order to avoid wasting the current.} Connect one wire from the 
cell to one post of the meter. Hold the other wire firmly against 
the other post and push the button for a moment. Note the total 



MEASURING ELECTRIC CURRENT 47 

amperage output of each cell. Connect the two cells in series ac- 
cording to instructor's directions, and measure the voltage, then 
the output in amperes with the thirty-five ampere ammeter and 
push button. When you have finished working with dry cells take 
the wires off immediately to avoid accidentally short-circuiting 
them. Screw the top off the push button and examine it. 

1. Make a table with two columns, one for volts and one for 
amperes. Record voltage and amperage output of cell No. i, 
cell No. 2, the two cells in series, and three cells in series. (NOTE. 
These meters give only approximate readings.) 

2. What is the correct voltage of a Leclanche cell? Same as 
dry cell. See Millikan, Gale and Pyle, or Ontario Physics. 

B. Meters. (Caution. Sensitive voltmeters and ammeters are 
easily ruined by attaching them to currents of too high voltage or too 
high amperage.) Expensive meters have very delicately balanced 
indicators. Ammeters should always be connected in series with 
some instrument as a lamp or motor, except in special cases like 
measuring the output of the dry cell with a meter of high amper- 
age scale. 

3. What might happen to an ammeter which registers only five 
amperes (five ampere scale) if it were attached to a new dry cell, 
or to the no-volt line without a lamp or some other instrument 
in series for resistance? A lamp or motor offers resistance and 
permits only a small amount of current (amperes) to flow. 

4. How many dry cells are needed to supply twelve volts? 

5. Diagram the proper number of cells in series to operate one 
six-volt lamp by means of a push button in the circuit. 

6. Operate a three-volt lamp by means of dry cells. Diagram 
the proper number of cells to operate two three-volt lamps in 
parallel by means of a single push button. 

C. Cells in Parallel. For special purposes dry cells are some- 
times connected in parallel (positive to positive and negative to 



48 LABORATORY PROJECTS IN PHYSICS 

negative). This produces the effect of a single cell of very large 
electrodes. The voltage is the same as that of one cell, but the 
amperage is increased according to the number of cells used. 

7. Diagram a circuit containing three cells in parallel, operating 
three lamps in parallel. See Mann and Twiss. 

BOOKS FOR SPECIAL STUDY: 

Physics Mann and Twiss. 
Physics Black and Davis. 
Physics Millikan, Gale and Pyle. 

21. ELECTRIC LIGHT AND POWER 

To construct and operate a miniature electric lighting and power 
system, and measure the current. 

MATERIALS. Two ring stands; two clamps; two crossbars of wood or 
glass each 5 in. long ; two dry cells ; No. 24 copper wire (insulated) ; three 
3-volt lamps ; small 3-volt motor ; electric bell ; battery voltmeter ; thirty-five 
ampere battery ammeter ; push button. 

A. Setting up a Miniature Wiring System. Using two ring 
stands as supports, attach two wooden crossbars by means 
of clamps. See instructor's model of the apparatus. To these 
crossbars lead two No. 24 insulated wires, each about i yard 
long. They should be fastened to holes in the crossbars. To 
the set of two cells connected in series, attach these wires. 
Care should be taken to keep the free ends of the wires 
from touching. With a knife remove the insulation from the 
wires at two opposite points, and hang a three-volt lamp across. 
You will find that this lamp does not let through as much current 
(amperes) as the cells can produce. Each lamp requires about a 
half ampere. The thirty-five ampere ammeter is not sensitive 
enough to measure the current used by a single lamp. 

i. How many amperes would three such lamps use? Attach 
three lamps in parallel on the line wires. Disconnect one of the 



ELECTRIC LIGHT AND POWER 



49 




50 LABORATORY PROJECTS IN PHYSICS 

wires at the battery and attach the ammeter in the circuit. See 
if three lamps cause it to register any current flow. 

2. If the total output of the two cells is fifteen amperes, how 
many such lamps could be operated at one time? Of course the 
battery would not last long at this rate of current consumption. 

E. Operating a Motor and a Bell. Operate a small electric 
motor from your line current. 

3. Connect the ammeter in series with the motor and note 
how much current it allows to pass through. 

4. How many such motors could be operated at one time 
with a set of cells delivering ten amperes? 

Attach an electric bell with a push button to the line and 
operate it. An electric doorbell usually requires about one-fifth 
of an ampere and three volts. 

5. Which is more expensive to ring a bell, or to light a lamp 
of the type used above ? Why ? 

6. How many dry cells are necessary to produce three volts 
pressure? six volts pressure? nine volts pressure? How should 
they be connected, in series or in parallel ? 

7. How might a cell or set of cells be short circuited and the 
current wasted? 

8. With respect to amperes, what does a short circuit mean? 

9. With respect to length of wire, how could a short circuit 
be avoided? 

10. With respect to kind of conductor, how could a short cir- 
cuit be avoided? What is meant by high resistance wire, or high 
resistance lamp? 

BOOKS FOR SPECIAL STUDY: 

Harper's Electricity Book Adams. 

Harper's How to Understand Electrical Work Onken. 

Physics Black and Davis. 



ELECTROMAGNETS AND PERMANENT MAGNETS 51 

22. ELECTROMAGNETS AND PERMANENT MAGNETS 

To study magnets and magnetism. 

MATERIALS. Dry cell; 3 ft. No. 24 insulated wire; large iron nail; 
small nails; compass; steel knitting rod ; pushbutton. 

N 




FIG. 22. Apparatus for the study of magnetism. 



Wind the wire around an iron nail, making about fifteen or 
twenty turns, connect it in series with the push button and note 
the effect on the small nails when ends of the wire are touched to 
a dry cell. (Caution. Do not let the current flow through this short 
wire for more than a moment, as it would soon ruin the dry cell.} 
With a compass, test for N. and S. poles of the magnet. The 
south pole of the coil will attract the north pole of the compass. 
Reverse the direction of current by interchanging the ends of the 
wires on the dry cell and retest for poles. 



52 LABORATORY PROJECTS IN PHYSICS 

1. How is the polarity affected by reversing the flow of current? 

2. Does a soft iron nail retain its magnetism when the current 
ceases ? 

3. State the law which applies to the attraction and repulsion 
of poles. These effects, discovered by Oersted, in 1819, have been 
the forerunners of such instruments as the electric bell, telegraph, 
telephone, dynamo, motor, etc. 

Place a hard steel knitting rod, or old file, in a large coil and send 
direct current from the no- volt line, a storage battery, or dry cells 
through the coil. Withdraw and test it for magnetism. 

4. What can you say of its permanency? Refer to texts. 

5. Should soft iron or hard steel be used in an electro- (tem- 
porary) magnet? What would be the objection to the other? 

6. The earth is a great magnet. Where are the earth's mag- 
netic poles? 

7. Distinguish between permanent magnets and electromagnets. 

8. Explain what a compass is and how it works. 

To increase the strength of an electromagnet, send a larger 
current (amperes) through the turns of wire around the bar, or 
keep the same current flowing and wind on more turns. The 
product of the amperes (current) and the number of turns deter- 
mine the magnetizing strength of the coil. Since electromagnets 
are more powerful than permanent magnets and since their mag- 
netism can be quickly destroyed, they have been given a great 
many practical applications, such as electric bells, electric motors, 
electric generators, induction coils, telegraph, telephone, wireless, 
etc. Electromagnetic cranes are used in lifting heavy masses of 
iron in steel mills and in the manufacture of nails, bolts, etc. A 
large magnetic crane will lift two tons of iron at one time. 

BOOKS FOR SPECIAL STUDY: 
Physics Black and Davis. 

The Boy Electrician Morgan. 

Elements cf Electricity Timbie. 

How to Understand Electrical Work Onken. 



THE ELECTRIC BELL AND THE TELEGRAPH 



53 



23. THE ELECTRIC BELL AND THE TELEGRAPH 

To study the operation of an electric bell. 

MATERIALS. Electric bell ; two dry cells ; No. 24 insulated wire ; push 
button. 

Ma/re and Break _ 







Dry Ce// 



FIG. 23. Path of the electric current in operating an electric bell. 



A. The Electric Bell. In the vibrating bell, when the circuit 
is closed as a result of pushing the button, there is an arrangement 
in the bell which alternately closes and opens the circuit through 
the coils. 

1. Diagram a bell, indicating the path of current through the 
bell by means of arrows. The path of the current is not exactly 
the same in all bells. See Mann and Twiss, Black and Davis, 
Millikan, Gale and Pyle. 

2. What caused the tapper to move toward the bell? 

3. What stops the flow of the current? 

4. What causes the tapper to move away from the bell? 

5. Diagram a circuit showing a battery, a push button, and a 
bell. 

6. Diagram a battery and one push button operating two 
bells. The bells should be attached in parallel. 



54 LABORATORY PROJECTS IN PHYSICS 

7. Diagram a circuit containing one battery and two bells, 
each bell being operated by an individual push button (front and 
back door). 

B. The Telegraph Receiving Instrument. An electric tele- 
graph instrument depends for its operation upon an electromagnet. 
An electric bell may be made to operate like a telegraph sounder 
(give a single stroke). Attach one wire from a battery to the 
proper post on the bell, and with the other wire, touch some other 
part of the bell so that the bell gives only a single stroke. (It 
should not vibrate.) 

8. Explain why it does not vibrate. In this operation the 
bell acts like a telegraph instrument. Attach the wires on the 
bell so that it makes a single stroke. Disconnect one terminal at 
the battery. Now as you make contact at the battery, the bell 
should act like a telegraph receiver. Examine a regular telegraph 
receiver (sounder). 

9. What causes the sounder-bar to move downward? 

10. What causes the sounder-bar to move upward? 

11. Why are bells and sounders made with two coils instead 
of one ? See Millikan, Gale and Pyle Electromagnet. 

BOOKS FOR SPECIAL STUDY: 
Physics Mann and Twiss. 
Harper's Electricity Book Adams. 
Practical Physics Black and Davis. 



ELECTROPLATING 55 

24. ELECTROPLATING 

To electroplate a piece of carbon with copper. 

MATERIALS. Battery jar used for the Liquid Cell ; carbon rod from a 
dry cell; strip of copper; copper sulfate; sulfuric acid; No. 24 insulated 
copper wires ; three- volt direct current from two dry cells. 

NOTE. This experiment may be performed more economically if a no- 
volt direct current is available by using a one-half ampere lamp as a resist- 
ance with each electroplating jar. If two dry cells are used do not fill the 
jar completely with copper sulfate solution. Fill it to a depth of about one 
inch. 

A. Copperplating Electrolyte and Wiring. Make up a copper 
sulfate electrolyte. Weigh 20 grams of copper sulfate crystals 
and dissolve in 300 c c. of water. Add about one c.c. of sulfuric 
acid. 

B. Wash the carbon thoroughly with scouring soap. (Caution. 
If no-volt direct current is used, be certain to connect a half ampere 
lamp for resistance in series, as shown in illustration.} Determine 
which terminal of the source of current is positive and which is 
negative, by attaching two wires and inserting the two ends into 
a tumbler of water containing about a quarter teaspoonful of 
table salt. If the current is of low voltage, use a small quantity 
of concentrated salt solution. The negative terminal gives the' 
greater evolution of bubbles. (Caution. Do not let these two 
wires touch, as a short circuit would result.} Attach the negative 
terminal of the line firmly to the carbon electrode, and the posi- 
tive terminal to the copper electrode. When the electrodes are 
properly attached, insert them into the solution of copper sulfate. 
Keep them as far apart as possible in order to prevent too rapid 
action. The carbon electrode should be turned at short intervals 
to insure an even deposit. If too much current is allowed to flow, 
the deposit will be spongy, or may contain some black oxide of 
copper. The best deposits are obtained when the action is very slow. 
Soon after inserting the electrodes, you should observe the grad- 



56 LABORATORY PROJECTS IN PHYSICS 

ual depositing of the copper. If the apparatus is working prop- 
erly the deposit should be a clean, brilliant copper color. Good 




FIG. 24a. Electroplating with dry cells. 

results may be obtained with a six-volt current and a fifth-ampere 
flow. The process of plating should require from fifteen minutes to 
a half hour. Better results are obtained when the operation is slow. 



Vo/ts 
current 




/amp res/stance 



FIG. 245. Electroplating with no-volt direct current. 



ELECT ROP LA TING 5 ^ 

C. The Operation. In the solution, the copper sulfate mole- 
cule separates into Cu ion and SCX ion. The copper is drawn 
toward the negative electrode and deposits upon the carbon. 
The SO4 ion is drawn to the positive electrode and there attacks 
the copper plate, forming new CuSO 4 . This action takes place 
as long as the electric current is flowing. The solution contains 
just as much CuSCX at the end as at the beginning. The pur- 
pose of the sulfuric acid is to reduce the concentration of the 
copper ion and prevent the formation of copper oxide. 

1. What was the purpose of the lamp in the circuit? 

2. An ampere of current deposits one gram of copper in fifty 
minutes. If, in your experiment, the carbon rod receives three- 
twentieths of a gram of copper in thirty minutes, how many 
amperes were flowing? 

D. Removing the Copper. When a good deposit is obtained, 
have the plated carbon approved by the instructor. Then in- 
terchange the electrodes on the wires, sending the current through 
the apparatus in the opposite direction. 

3. Explain chemically what happens when the current is re- 
versed. 

4. Make a careful diagram of the apparatus and wiring. 

5. How may knives and spoons be plated with silver? See 
Black and Davis, or' Millikan, Gale and Pyle, or Ontario Physics. 

6. In charging a storage battery, what compound of lead is 
formed on the positive plate? See Hoadley, Millikan, Gale and 
Pyle, or Black and Davis. When the storage battery is discharged, 
this deposit reacts with the solution in a manner similar to the 
action of a liquid cell. 

A lead paper-weight may be copperplated as described above. 
Gold, silver, nickel, cobalt, platinum, and brass are among the t 
metals that may be plated by the electrolytic process. A standard 
silverplating solution consists of potassium cyanide and silver 



58 LABORATORY PROJECTS IN PHYSICS 

cyanide. The cyanide salts are more suitable electrolytes for 
rapid work, but they are dangerous on account of their poisonous 
properties. An object to be electroplated should be chemically 
clean. It should be thoroughly washed in both acid and alkali 
to remove every trace of foreign matter. 

BOOKS FOR SPECIAL STUDY: 

Physics Millikan, Gale and Pyle. 
Practical Physics Black and Davis. 
Harper's Electricity Book Adams. 



25. PINHOLE IMAGES 

To study images projected through a pinhole. 

MATERIALS. A cardboard having a pinhole and a large hole of one- 
quarter inch diameter, the two holes being located about two inches apart; 
small candle ; cardboard for screen. 





FIG. 25. An image may be produced by light rays passing from a candle-flame through 

a pinhole. 

Place a lighted candle in front of a piece of cardboard in which 
a small hole (as large as a pin head), has been punched. Hold a 






PINHOLE IMAGES 



59 



second piece of cardboard (screen) behind the first and observe 
the images formed on the screen by the light rays which pass 
through the small hole. The infinite number of points which con- 
stitute the flame may each be considered a source of radiation 
from which light waves pass out in all directions. For simplicity 
in making diagrams, radiant energy may be represented as straight 
lines traveling in all directions from each point-source of illumi- 
nation on the flame. 

1. How does moving the screen farther back affect the image 
with respect to (a) size, (b) brightness? 

2. How does moving the object (flame) farther from the small 
opening affect the image with respect to (a) size, (b) brightness? 

3. Try a larger opening. What effect has the larger opening 
upon the image with respect to (a) sharpness, (b) brightness? 

4. Any number of light rays may cross at a point without 
undergoing change of direction. How does the fact that light rays 
travel in straight lines explain why the image is inverted? Make 
a simple diagram of the flame, the opening and the image with 
straight lines representing the rays of light. Reference, Mann 
and Twiss. 

5. Explain the fact that a small opening makes a sharper (less 
blurred) image than a larger one. 

6. Explain the fact that a large opening makes a brighter image. 

7. Diagram a pinhole camera. See Hoadley. 

BOOKS FOR SPECIAL STUDY: 
Physics Mann and Twiss. 
The Wonder Book of Light Houston. 
General Science Hodgdon. 



60 LABORATORY PROJECTS IN PHYSICS 

26. LENS IMAGES 

To study images projected by means of a lens. 
MATERIALS. Small candle ; convex lens ; screen. 

A pinhole may be considered as permitting only a few rays 
from each point on the flame to pass through the hole, casting 
its illumination on the screen. A lens, on the other hand, receives 




/mage 
Object Lens on 3 screen 

FIG. 26. How light rays from two points on a flame are focused by a lens producing 

an inverted image. 

many more rays from each point on the flame and focuses them to 
corresponding points on the screen. It should be remembered 
that light travels by means of waves. Rays, or lines, are used for 
convenience and simplicity. Thus each one of the infinite num- 
ber of points on the flame is represented by a corresponding point 
of illumination, which is produced on the screen by the refraction 
and focusing of the light rays. The accompanying diagram shows 
how the lens receives light from two such points. Two 'cones of 
light radiation strike the face of the lens and are focused to two 
points on the screen. For convenience in diagraming, the cone of 
radiation from each point is represented by simply three lines. 

Place the lens between the candle and the screen and move 
the candle and screen into such positions that a sharply focused 
image is formed. 



LENS IMAGES 6l 

1. Move the candle and the screen so that the image is the 
exact size of the object. How do the distances of the object from 
the lens and of the image from the lens compare when the object 
and the image are equal in size? What is this distance in inches 
in the case of this particular lens? 

2. How does the lens image compare with the pinhole image with 
respect to (a) brightness, (b) sharpness ? Explain these differences. 

3. Diagram two cones of light radiation proceeding from two 
points on the flame striking the surface of the lens and being 
focused to two points on the screen. This may be represented 
by three lines of light from each point, one through the center of 
the lens with no change of direction, and two rays striking near 
opposite edges of the lens and refracted to a common point on the 
screen. See illustration. 

4. If the lens remains stationary and the screen is moved 
farther away, what change in the position of the object must be 
made to produce a sharp image ? What change does this make 
with respect to size and brightness of the image? 

5. If the lens remains stationary and the screen is moved closer 
to the lens, what change must be made to produce a sharp focus ? 

6. Is it possible to place the object and the screen in a stationary 
position and focus by moving only the lens? In focusing the 
ordinary camera and the projection lantern, what is moved? 

7. Diagram object, lens, and image, showing proper proportions 
of object and image when the object (flame) is placed closer to 
the lens than in No. i. 

8. Diagram object, lens, and .image, showing proper propor- 
tions of object and image when the object (flame) is placed farther 
from the lens than in No. i. 

BOOKS FOR SPECIAL STUDY: 
Physics Mann and Twiss. 
How to Make Good Pictures Eastman Kodak Co. 
The Wonder Book of Light Houston. 
Photography of To-day Jones. 



62 



LABORATORY PROJECTS IN PHYSICS 



27. LAW OF REFLECTION 

To prove that when light is reflected from a mirror the angle 
of incidence equals the angle of reflection. 

MATERIALS. Nickel-plated mirror ; two small candles ; two pins ; sheet 
of paper ; protractor. 

Mirror 




FIG. 27. Diagram showing the path of light rays from two candle flames striking a 
mirror and being reflected to the eye of an observer. 

Stand the mirror near the center of the sheet of paper facing 
toward the bottom, and draw a line along the front of the mirror 
representing its edge. Draw a second line from one of the lower 
corners till it strikes the mirror line at about its midpoint. Stand 
two small candles, each about one inch long, on the paper about 
four inches apart, with their centers directly over the line which 
strikes the mirror. Now place your eye in proper position to 



LAWS OF REFLECTION 63 

observe the images of the candles and the line in the mirror, so 
that the image of one candle appears directly behind the other. 
Continue the image of the candle line by a line on the paper from 
the mirror toward your eye. The two lines should intersect at 
the edge of the mirror. When the eye is in position near the level 
of the paper, the lines drawn represent the path of light rays 
coming from the candles to the eye. Light from the candles has 
struck the mirror and has been reflected in the direction of the 
line toward the eye of the observer. This reflection of the rays 
of light causes the light to appear to come from beyond the mirror, 
where the candles appear to be located. The candles appear to 
be as far back of the mirror as they actually are in front of it. 

1. Using the protractor, erect a perpendicular at the point 
where the two lines strike the mirror. Measure in degrees on the 
protractor the angle of incidence and the angle of reflection 
(angles between the oblique lines and the perpendicular), and 
note how angle BOA compares in size with angle BOC. Read 
texts on reflection. 

2. Repeat the experiment by changing the size of the angles 
and make a new set of measurements. NOTE. This experiment 
may be done with pins in place of the two candles as directed 
above. 

3. If the angle of incidence is made larger, how does this affect 
the angle of reflection? 

4. When you stand at the left of a mirror which hangs on the 
wall, in what position must a second person stand in order that 
you may see each other in the mirror ? 

5. When a mirror hangs perpendicularly on the wall, what is the 
highest point between the level of the observer's eyes and the floor 
at which the bottom of the mirror may be placed in order that he 
may see his feet in the mirror ? Test it. Make a diagram as proof 
of your conclusion. 

6. Diagram a ray of light from an object striking the surface 



64 LABORATORY PROJECTS IN PHYSICS 

of a mirror and being reflected to the eye of an observer. See 
Household Physics, Butler, or Ontario Physics Reflection. 

7. Diagram rays of light from a tree on one bank of a pond 
striking the water and being reflected to the eye of an observer, 
showing how the rays may cause the tree to appear inverted in 
the water. 

8. Diagram light rays reflected to a focus by a parabolic mirror. 
See Black and Davis, or Carhart and Chute. 

Objects appear to be located in the direction of the last straight- 
line-path of light approaching the eye. No matter how many 
times the direction of light rays from an object have been changed 
by reflection or refraction, the eye receives the light as if the object 
were located in the direction of the rays which finally enter the eye. 

BOOKS FOR SPECIAL STUDY: 
General Science Barber. 
Physics Black and Davis. 

28. THE LAW OF INTENSITY 

To prove that if the distance of an object from a light source is 
doubled, the light which strikes a given area on the object 
is one-fourth as intense. 

MATERIALS. Candle flame ; card with hole one inch square ; cardboard 
screen scored with sixteen one-inch squares ; ringstands and clamps. 

Law of Intensity. The intensity of illumination varies in- 
versely as the square of the distance from the source of light. 
The area of the surface illuminated varies directly as the square 
of the distance. 

Place the card with one-inch square hole one foot from the 
flame, and the screen one foot beyond the first card (two feet 
from the flame). The light from the candle will shine through the 
one-inch opening and illuminate the screen. 

i. Measure the area of the space illuminated on the screen 
when the screen is twice as far from the source of light as the one- 



THE LAW OF INTENSITY 



inch hole. Note that the light which passes through the one- 
inch hole spreads to four times the area of the hole. 

2. Move the screen three times as far away from the flame as 
the one-inch hole and demonstrate the law. State the result 
with regard to intensity for this distance. State the result with 
regard to the surface illuminated. 

3. How does the intensity of illumination two feet from a 
source compare with the intensity eight feet from the same source ? 




F/ame One inch Scored 

square ho/c card board screen 

FIG. 28. Diagram showing the areas covered by light which passes through a one- 
square-inch opening. 

4. In a school room or home, how does the illumination which 
a book receives from a window at a distance of four feet, com- 
pare with the illumination which the book receives from the same 
window at a distance of twelve feet? The law applies here ap- 
proximately the same as for a candle. If in this case the distances 
are as one to three, how do the intensities of illumination compare? 

5. Make a diagram showing how light radiates from a point- 
source through a one-inch square opening, one foot from the 
source. Show the surface illuminated at two feet, at three feet, 
and at four feet. 

BOOKS FOR SPECIAL STUDY : 
General Science Hodgdon. 
Modern Illumination Horstmann and Tousley. 



66 LABORATORY PROJECTS IN PHYSICS 

29. THE PRISM AND THE LENS REFRACTION 

To demonstrate the refraction of light at the surfaces of a 
glass prism. 

MATERIALS. Glass prism; rule; protractor; sheet of paper; double 
convex lens (reading glass lens). 

From about the middle point on the upper edge of the paper, 
draw a straight line half way down the page. Stand the prism 
on its triangular end so that the line at the middle of the page 
strikes the middle point of one edge obliquely (not perpendicu- 
larly). With your eye near the level of the paper, sighting from 
one of the lower corners, turn the prism slightly until you ob- 
serve the original line through the prism as if it came from the op- 
posite upper .corner. It will have a faint color fringe. Con- 
tinue it from the lower edge of the prism toward your eye, so 
that it appears through the prism as a continuous straight line 
toward the lower corner of the page. Draw the outline of the 
base of the prism on the paper. Draw the path of light as it 
passes between the edges of the prism. 

Explanation : Any visible object is seen by reason of light rays 
coming from it to the eye. When the eye sees the line through 
the prism, it is due to the fact that the light rays are coming from 
the line through the glass to the eye. If the line appears to be 
in some unexpected direction, it must be due to a change in direc- 
tion of the light ray caused by its passing through the prism. 

i. Extend the first line and with a protractor measure in 
degrees how much the prism refracts the light ray from its original 
course. Explain the cause of refraction. See Carhart and Chute. 
If convenient, hold the prism in the sunlight and see how the sun's 
rays, which strike it, are thrown out of their course. Note that 
the refracted rays are not white light, but the prismatic colors. 
When a light ray is refracted by a simple prism, or lens, it also 
undergoes dispersion into its component color rays. 



THE PRISM AND THE LENS REFRACTION 67 



\2?/rec//o/7 fro/n 
^ wh/'ch //ant 

to co/ne. 



J2/rect/on from 

tfie //yht y/'ven off by 

the fine actua//\ 




D/rect/'on of 

the //oht after 

refracted 



29. - A light ray is refracted by a prism causing it to appear to the eye to 
from a different direction. 



68 LABORATORY PROJECTS IN PHYSICS 

2. What is meant by the term dispersion? See texts. 

3. Is a light ray refracted toward the thicker part or toward 
the thinner part of the prism? 

4. A lens may be considered as being composed of an infinite 
number of small sections of glass with non-parallel sides (prisms). 
When the lens is held in the path of parallel rays (sunlight), in 
which direction are rays which strike above the center refracted? 

5. In which direction are rays which strike below the center 
refracted ? 

6. What is the name of a point beyond the lens at which all 
of the rays cross? Refer to texts. 

y. What is meant by the focal length of a lens? Refer to 
texts. . . 

8. Does a thick lens refract more or less than a thin lens? 
Explain. 

9. What form of lens has a long focal length? A short focal 
length? 

10. Make two diagrams illustrating the answers to No. 9. 
Show lenses refracting parallel rays. 

BOOKS FOR SPECIAL STUDY: 
General Science Hodgdon. 
General Science Barber. 
Photography of To-day Jones. 
Physics Hoadley. 



THE GLASS CUBE AND THE LENS REFRACTION 69 



30. THE GLASS CUBE AND THE LENS REFRACTION 

Refraction at the surface of a glass cube and" at the surface of 

a lens. 

MATERIALS. Glass cube; rule; paper; reading glass lens (double 
convex). 

Beginning at the upper left corner of the paper, draw a diagonal 
half way across the paper. Place the cube on this line, at about 
the center of the page, so that its sides are parallel to the edges 
of the paper and the diagonal strikes the upper edge of the 
cube about a quarter of an inch from the upper left corner. 
Draw the outline of the cube. Now with your eye on the level 
of the paper, sighting from the lower right corner of the paper, 
observe the original line through the cube and continue it from 
the lower edge of the cube toward your eye so that it appears 
through the cube as a continuous straight line. Draw the path 
' of light as it passes between the edges of the cube. 

Repeat the experiment with the original line striking the cube 
at the middle point of one edge and perpendicular to it. 

1. What happens to light rays when they enter the glass at an 
oblique angle (not perpendicular) ? 

2. If a light ray passes perpendicularly from air through a 
glass object with parallel sides, is its direction changed? 

3. If a light ray passes from air through a glass object with 
non-parallel sides, how is its course affected? 

4. Draw cross sections of a double convex lens and a plano- 
convex lens. See Hoadley. 

5. Explain the fact that the light ray (wave) which strikes 
perpendicular at the center of a lens, passes through without 
being deviated from its original direction. See Black and Davis 
Refraction. 



LABORATORY PROJECTS IN PHYSICS 



Direction 

from which 

Sight given off \ 

by the /ine appears x N 

to come ss if en/ers \ 

the eye. 



Direct/on from which 

the fight given off by 
\ \ /he /ine actuaS/y comes. 




Eye of 
Observer. 

^ . A light ray is refracted when it enters a glass cube at an oblique angle (not 
perpendicular). It is again refracted when it passes out at the opposite side. 



THE GLASS CUBE AND THE LENS REFRACTION 71 

6. What happens to a light ray (wave) which passes through 
any point other than the center? See Black and Davis. 

7. In what region of a lens does the greatest refraction occur? 
Explain. 

8. Draw a lens and show three rays of light striking it from 
some one point, illustrating any refraction that may take place. 
Show one ray passing through at the center and the others near 
two opposite edges. 

9. Diagram a lens showing how the lens affects parallel rays 
as in the case of rays from the sun. 

NOTE : In cases of refraction the bending of the light ray takes 
place at the surface, not inside the glass. Note, also, that refraction 
is greater if the approaching ray enters the glass more obliquely. 
Refraction occurs, in general, when a light ray passes obliquely 
from one medium to another of different optical density. Re- 
fraction occurs as the ray enters the glass and again on the oppo- 
site side as it leaves the glass. The eye, in seeing, assumes that 
an object is in the direction of the light ray which immediately 
enters the eye, regardless of any previous refractions of the ray. 

BOOKS FOR SPECIAL STUDY: 

General Science Hodgdon. 

Physics Hoadley. 

Light, Visibile and Invisible Thompson. 



LABORATORY PROJECTS IN PHYSICS 



31. ILLUMINATION AND LIGHTING 

MATERIALS. 5 small candles; ring stand; clamp; white cardboard 
screen ; ruler ; wood blocks for candles ; dark room. 



Shadow cast 
| by cand/eB. 

I Shadow cast 






Cardboard 
screen 



Cancf/esA 

FIG. 31. A Rumford photometer a simple device for comparing the brightness 
of one light source with another. 

A. Intensity of Light in Relation to Distance from its Source. 

Set up the white cardboard screen vertically, and place the 
upright rod of the ring stand about three or four inches in 
front of it. Two feet from the screen place a block with four 
candles (^4) arranged one behind the other with respect to the 
screen. See instructor's model. A shadow will be cast on the 
screen back of the ring stand rod. Place a single candle (B) in 
such a position that another shadow from the same rod will be cast 
close to the previous shadow. Note that candles (^4) illuminate 
(shine upon) the shadow of candle (B), and that candle (B) illu- 
minates the shadow cast by candles (^4). 

1. When the two sources of light are placed equidistant from 
the screen, if the shadow cast by the four candles (^4) is illu- 
minated less than that cast by the one candle (B), which source 
gives the more light to the screen? 

2. How will the shadows compare in brightness when the screen 



ILLUMINATION AND LIGHTING 73 

receives equal illumination from the two sources ? This device is 
known as a Rumford Photometer. 

3. When the shadows are equally illuminated, measure the 
distance from each source of light to the shadow which it illu- 
minates, not the one which it makes. 

4. If a source of light is moved twice as far away from an object, 
how much brighter must the light be made to illuminate the 
object to the same degree as before? 

5. If A reads a book at a distance of three feet from a table- 
lamp and B reads a book at a distance of six feet from the same 
lamp, how do their illuminations compare? 

6. State the Law of Inverse Squares with respect to intensity 
of illumination. See Mann and Twiss, Hoadley, or Black and 
Davis. The same law applies to the intensity of sound, the 
attraction of gravitation, and magnetism with respect to distance. 

B. Indirect Lighting. When electric lamps or gas lamps 
are fitted with reflectors, placed underneath for throwing an 
intense illumination evenly over the white ceiling of a room, the 
effect is known as indirect lighting. In this case the light from 
the lamp is not visible directly, but by reflection from the ceil- 
ing. This lighting scheme supplies a soft and pleasing effect, but 
it requires a large amount of light and is, therefore, expensive. 

C. Semi-indirect lighting results from the use of large orna- 
mental glass diffusing shades, placed under a brilliant electric, or 
gas lamp. This system has met with great popularity in recent 
years in home lighting as well as for other special lighting pur- 
poses. 

D. Direct lighting refers to the older method of obtaining illu- 
mination directly from the light source. 

BOOKS FOR SPECIAL STUDY: 

Modern Illumination Horstmann and Tousley. 
Practical Physics Black and Davis. 
General Science Barber. 



74 LABORATORY PROJECTS IN PHYSICS 

32. CANDLE POWER AND FOOT-CANDLES 
To measure the candle power of a lamp. 

MATERIALS. Candle; ring stand; white cardboard screen; ruler; 
block ; small 3- volt incandescent lamp ; two dry cells ; dark room. 

A . Photometer. Set up a Rumf ord photometer as described in 
experiment No. 31. See instructor's model. Substitute for the 
four candles a small incandescent lamp connected with a two- 
cell battery. Adjust until the one candle and the small incan- 
descent light shine, as nearly as you can judge, with equal 
intensity upon the shadows. If the two light sources to be com- 
pared give lights of different colors, as in this case, the judging of 
equal intensity will be more difficult than when the lights are of the 
same color. Make three or more independent judgments and 
average the results t 

1. Compute the candle power of the lamp. (Their candle 
powers will compare directly as the squares of their distances 
from the screen.) 

2. A candle stands one foot from the screen and a large electric 
lamp stands ten feet from the screen. If the shadows produced 
by the two sources are equally illuminated, what is the candle 
power of the lamp? 

B. Light and Illumination. The arrangement, the number, as 
well as the kind of lights, to be used in various rooms must be 
considered in the problem of room lighting. There are two gen- 
eral factors in any lighting scheme; the brightness of the lights 
themselves (candle power) which makes looking at them either pain- 
ful, or tolerable to the eye ; and the illumination given to a room, 
which is gauged by the clearness with which the objects in the 
room can be seen. A light source may be very bright (of great 
candle power) and yet it may not illuminate properly because 



CANDLE POWER AND FOOT-CANDLES 75 

of misdirected rays, improper shades, the color of the walls, or other 
light-reflecting or light-absorbing agencies. The intensity of the 
light which falls upon an object is measured in foot-candles. A 
foot-candle is the intensity at a distance of one foot from a source 
of light of one candle power in value. At a distance. of two feet, 
according to the law of inverse squares this same source would 
give an intensity of only \ foot-candle, at three feet, ^ foot-candle 
and so on. 

C. Rules for Determining Candle Power and Foot-candles for 
Reading. Three foot-candles of light are considered adequate in- 
tensity for ordinary reading purposes. 

To find the foot-candles which fall upon an object, divide the candle 
power of the source by the square of the distance in feet which the ob- 
ject is from it. 

To determine the candle power of the lamp to be used for reading, 
square the distance from the lamp and multiply by three. 

To determine how far to sit from a lamp for reading, divide the 
candle power of the lamp by three and extract the square root. 

3. What intensity in foot-candles would be supplied for reading 
by a 1 6 candle power lamp at a distance of 4 feet? Two feet? 

4. If a 3 candle power lamp is adequate for reading at a dis- 
tance of one foot from the lamp, what candle power should be 
provided for reading at a distance of five feet ? 

5. How far from a forty-eight candle power lamp should one sit 
for reading ? 

BOOKS FOR SPECIAL STUDY: 

Modern Illumination Horstmann and Tousley. 
General Science Barber. 
General Science Hodgdon. 
Practical Physics Black and Davis. 



76 LABORATORY PROJECTS IN PHYSICS 



33. COLOR 

To determine the composition of sunlight and study the spectrum 

colors. 

MATERIALS. Glass prism; ring stand and clamp; reading glass lens; 
cardboard screen. 




Cardboard Lens 

screen Prism 

FIG. 32. The prism refracts and disperses the light. The lens combines the color 
rays again, producing white light analysis and synthesis of sunlight. 

A. Analyzing Sunlight. The Prismatic Colors. Set the prism 
horizontally in a ring stand clamp in the sunlight, so that one 
of the long edges points downward. Place paper or rubber 
tubing between the prism and the clamp to protect the glass. 
The white sunlight which strikes one face of the prism will be 
broken up into its component colors. These colors represent the 
different vibration rates which combine to make sunlight or 
white light. Hold a cardboard screen in the path of these 
colors, about six or eight feet from the prism. Darken the 
room as much as possible. 

1. What three general color effects do you notice? These 
colors shade off into various other tints. What are the three 
primary colors? See Carhart and Chute, Millikan, Gale and 
Pyle, Mann and Twiss. 

2. Name the seven colors of the rainbow as ordinarily listed. 
Hold a lens in front of the screen in the path of these color rays 
at the proper distance from the screen to bring them to a focus 
and reunite them on the screen. 



COLOR 77 

3. What is the color of the image? 

4. What conclusion do these facts suggest regarding the nature 
of sunlight? See Millikan, Gale and Pyle, Carhart and Chute, 
Black and Davis. When the colors are focused to white light on 
the screen, note that you have on the screen an image of the illu- 
minated prism, rectangular in shape. 

5. What is the distance in inches from the image to the lens? 

6. When the screen ' is moved further back from the point 
of focus, what changes do you note in the order of colors? 
Explain. 

7. Which color of light does the prism refract more, blue light 
or red light? Blue light represents a vibration rate about twice 
as rapid as red light. Light waves produced by the more rapid 
vibration rates are refracted more than those from slower vibra- 
tion rates. 

B. Color. Colors are produced by the effects of different vibra- 
tion rates upon the optic nerve. The visible colors range from 
the violet at one end of the spectrum to the red at the other end. 
The vibration rates which produce these effects range from ap- 
proximately four hundred million million per second for red light, 
to seven hundred million million per second for violet light. Other 
radiation such as heat is too slow to be seen, while ultra violet 
light and X-rays are too rapid to be seen by the eye. 

Different light sources such as sunlight, gas light, lamp light, 
electric light, all represent different combinations of colors. Arti- 
ficial lights in general have less blue than sunlight. The mercury 
vapor lamp, however, is an exception to this rule. It gives a greater 
percentage of blue than sunlight. 

BOOKS FOR SPECIAL STUDY: 
Physics Mann and Twiss. 
General Science Hodgdon. 
Light , Visible and Invisible Thompson. 
Physics Hoadley. 



78 LABORATORY PROJECTS IN PHYSICS 

34. ABSORPTION AND LIGHTING 
To study absorption of colors. 

MATERIALS. Glass prism ; ring stand and clamp ; cardboard and screen ; 
transparent gelatine color-screens, red and blue ; red cloth and blue cloth. 

A. Color Absorption. Place a red transparent gelatine sheet in 
the path of the color rays from the prism as set up in the preced- 
ing experiment. If one gelatine sheet is too thin combine several 
sheets. 

1. What color or colors are absorbed when white light passes 
through a red transparent medium? 

2. When sunlight strikes a piece of red cloth, which of the 
prismatic colors are absorbed? Which is reflected? 

3. Use pieces of blue gelatin and pieces of blue cloth and 
explain. In the same way try any other colors that are available, 
and explain the results. 

4. What causes a blue object to look blue in sunlight ? Which 
of the three prismatic colors, red, green and blue, does a red 
transparent sheet, or screen, placed in front of a blue piece of 
cloth absorb? If sunlight had no blue rays in it, how would a 
blue cloth appear? 

5. What colors are absorbed by a piece of blue cloth? 

6. If all other light is cut off from a blue cloth, except what 
comes through a red transparent screen (red light), why does the 
blue cloth tend to look black ? 

7. Place a piece of blue cloth or a blue gelatine sheet under a 
red gelatine sheet and observe its color. Explain. 

8. What effect would blue walls, blue window glass, and blue 
lamp shades, have upon the color of a red dress? 

9. What effect would red walls, red window glass, and red 
lamp shades have upon the color of a blue dress ? 

10. Incandescent electric, gas and oil lights are generally defi- 



ABSORPTION AND LIGHTING 79 

cient in blue rays. What effect has this upon, the color of a blue 
dress ? 

11. When observed in ordinary artificial light, why do some 
colored articles of cloth appear different from their appearance 
in daylight? 

12. If it were possible to get artificial light with the same color 
proportions in it as sunlight, what advantage would be obtained 
in observing colors? This effect is now obtained almost per- 
fectly by combinations of colored lights with color absorption 
globes. 

B. Color Photography. One successful method of producing 
color photographs involves taking three different exposures through 
different transparent color screens (red, yellow, blue). The three 
negatives thus obtained are used for making three color prints 
of the three colors red, yellow, blue. When these three color 
prints are superimposed the result is a beautiful photograph in 
natural colors. The Lumiere Autochrome Plates represent another 
method of color photography. The picture is produced directly 
on a plate which has been especially treated with an emulsion 
containing fine starch particles of red, green, and blue. The color 
photograph is developed directly on this plate and cannot be re- 
moved from it. It must be observed by holding it up toward the 
light or by hanging it against a window. 

BOOKS FOR SPECIAL STUDY: 

General Science Hodgdon. 

Photography of Today Jones. 

Modern Illumination Horstmann and Tousley. 



8o 



LABORATORY PROJECTS IN PHYSICS 



35. TUNING FORK AND VIBRATING AIR COLUMN 

To determine the rate of vibration of a tuning fork (number of 
vibrations per second) by means of a vibrating air column. 

MATERIALS. Hydrometer jar ; lamp chimney ; tuning fork ; ring stand. 




FIG. 33. An air column of proper length vibrates in sympathy with a tuning fork. 

A. Determining the Pitch of a Tuning Fork. Fill the jar 
nearly full of water. Support the lamp chimney on a ring stand 



TUNING FORK AND VIBRATING AIR COLUMN 8 1 

so that one end reaches into the water. This furnishes an air 
column closed at one end (by water). At the same time it is 
possible to increase or decrease the length of the air column by 
raising or lowering the chimney in the water, 

When a tuning fork vibrates at the mouth of such an air column 
the tone of the fork may be loudly reinforced. This reinforcement 
occurs only when the proper length of air column is obtained. 
Move the chimney up and down till you find the exact length 
of air column which gives the loudest response to the tone of 
the fork. If the air column is comparatively narrow, this defi- 
nite length furnishes a basis for determining how many vibra- 
tions the fork makes per second. Measure very carefully the 
distance between the top of the glass tube and the water 
level. Add one-third of the inside diameter of the tube as a 
correction for the width of the air column. Multiply this re- 
sult by four, reduce to feet and divide into eleven hundred and 
thirty feet (the velocity of sound per second in air). This result 
is the vibration rate per second of the tuning fork. Make three 
separate determinations as a check to your work and average 
the results. 

B. Explanation. The air column in a tube closed at one end 
acts like a coil spring fastened firmly at the bottom. If the air 
column is of just the proper length it can vibrate at the same rate 
as the fork and reinforce the fork. The air column vibrates in 
sympathy with the fork and makes the tone louder. A sound 
wave travels down the air column, strikes the water, rebounds, 
and returns to the top of the tube in the time of half a vibration 
of the fork. Sound, therefore, travels twice this distance down and 
back in the time of a complete vibration of the air column. This 
means that sound travels four times the length of the tube in each 
vibration of the air column and of the fork. In a second, then, 
there are as many vibrations as this distance is contained in eleven 
hundred and thirty feet. 



82 LABORATORY PROJECTS IN PHYSICS 

1. What length of air column reinforces the fork which you 
used? 

2. What is the vibration rate of the fork which you used accord- 
ing to your calculations? 

3. How far does sound travel in the time of one vibration of 
this fork? Include correction for diameter. 

4. What is meant by the wave length of a tuning fork? See 
Mann and Twiss, Carhart and Chute, or Ontario Physics. 

5. Does a fork of high pitch require a long tube or a short tube 
for reinforcement? Explain. 

6. Does striking a tuning fork harder change its pitch? How 
could you prove this? 

7. If a tuning fork vibrates five hundred and twelve times per 
second what length of air column is required to reinforce it? 
Disregard width of air column. 

8. Diagram the apparatus used in this experiment. 

If a flat stream of air is directed properly across the end of this 
air column it will set the air in vibration similar to that of an 
organ pipe. As an organ pipe or whistle it will produce the same 
tone as the fork, provided the air column has the same length 
as that which reinforces the fork. 

9. What kind of pitch would you expect to obtain from a very 
long pipe-organ pipe? 

BOOKS FOR SPECIAL STUDY: 

General Science Hodgdon. 
. Physics Hoadley. 

Sound and Music Blaserna. 



THE VIBRATING STRING 83 

36. THE VIBRATING STRING 
To study musical tones produced by a vibrating string. 

MATERIALS. 3-foot ring stand; No. 22 piano wire, length thirty-one 
inches, with one-inch rin^s attached at the ends; six screw clamp holders; 
yardstick. 



8 8 




FIG. 34. Apparatus for studying the vibrating string. 



A. Mounting the String. Lay the ring stand down lengthwise 
on the table. Screw one clamp holder tight against the bottom 
of the stand rod. Put a second clamp holder on loose at the top 
of the stand rod. If the thumb-screw of the top clamp holder 
is loose enough it will lean toward the bottom when the ring is 
slipped over it and stretched tight. (Caution. Keep your eyes at 
a safe distance from the string, as there is danger of injury in case 
the string should break.) Tighten the upper clamp and as the 



84 LABORATORY PROJECTS IN PHYSICS 

clamp holder straightens into position the string should become 
tight. If you have any difficulty in making the string tight, ask 
the instructor to help you. Place two other clamp holders near 
the first two so that the string is exactly thirty inches long between 
the last two clamp holders. Clamp them tight and turn them 
so that they press upon the string at two points exactly thirty 
inches apart. The string should then give a clear musical tone 
when picked. This experiment should be performed with the 
apparatus resting upon a wooden table top. 

1. What causes sound and by what means is it transmitted 
to the ear? See Carhart and Chute, or Hoadley, or other text. 

2. Compare the respective causes of a musical tone and a 
noise. Explain. 

3. What technical name is applied to the kind of vibrations 
which produce musical tones? 

4. Mention one other method of producing tones aside from 
vibrating strings. 

5. With respect to the cause of the tone, how does a tone of 
low pitch differ from one of high pitch ? 

6. What is the vibration rate per second of a string which gives 
the pitch Middle C? (Standard pitch.) See Millikan, Gale and 
Pyle, Hoadley, or Carhart and Chute Musical Scale. 

7. When a string is picked vigorously (very loud) what evi- 
dence have you that it vibrates at the same rate as when it is 
picked lightly? 

B. Loudness. 

8. Explain the fact that a string picked harder produces a 
louder tone. What causes loudness? 

9. Lift the apparatus from the table and pick the string. Do 
you notice a difference in loudness when the apparatus is held 
in your hand? Explain. See Carhart and Chute Resonance. 

10. What parts of the following instruments serve to intensify 
the tones piano, guitar, Victrola? 



THE VIBRATING STRING 85 

C. The Pitch of a String. 

11. Place a clamp holder at the middle of the rod, dividing the 
string into two parts of fifteen inches each. Pick the string. 
The musician calls this tone an octave higher. What does the 
term octave mean with respect to vibration rate? State the law 
which applies to the length of a string? Name two instruments 
which illustrate this law. See Carhart and Chute Laws of 
Strings. 

12. How is the vibration rate affected by (a) tension, (b) thick- 
ness, (c) weight ? Refer to texts. 

13. Place a clamp holder at a point one- third of the distance 
between the two ends, dividing the string into two parts, one ten 
inches long, the other twenty inches long. How are these tones 
related with respect to vibration rate? 

14. Using two clamp holders, divide the thirty-inch string into 
three parts, twelve inches, ten inches, and eight inches. Sound 
these three lengths of strings in succession. What are the names 
of these three notes? If you do not know, ask a musician in the 
class. How are the vibration rates of these tones related mathe- 
matically? See Carhart and Chute Laws of Strings. 

BOOKS FOR SPECIAL STUDY: 
Physics Hoadley. 
General Science Hodgdon. 
Household Physics Butler. 
Sound and Music Blaseraa. 



86 



LABORATORY PROJECTS IN PHYSICS 



GROUP II. EXPERIMENTS 

37. BLOOD PRESSURE 
To determine the pressure of the blood. 

MATERIALS. Manometer tube with millimeter scale ; two pieces of rubber 
tubing ; small air pump ; T-tube ; screw clamp ; pressure sleeve ; mercury. 



Manometer 
containing Afercury. 



\ fnflating bu/b 

with contro/ vo/ve. 




FIG. 35. Measuring blood pressure. 

A. Setting Up the Apparatus. The U-tube should be half full 
of mercury. Attach the T-tube to a clamp on a ring stand. Con- 
nect the arm of the U-tube to the T-tube by means of a rubber 
sleeve and to the third arm attach an air pressure pump. The 



BLOOD PRESSURE 87 

pressure bag consists of a rubber bag ten inches long and six inches 
wide covered with cloth. 

NOTE : If the pressure sleeve is made similar to that shown in 
the illustration the T-tube should be omitted. 

B. Applying the Sleeve. Sit completely relaxed in a chair. 
Place the part of the sleeve containing the rubber bag on the 
inside of the left arm above the elbow. (Ordinarily it is not 
necessary to bare the arm.) Wrap the remainder of the sleeve 
around like a bandage and tuck the end under the preceding fold. 
Pump enough air into the bag to cause the pulse to disappear. 
(About 200 millimeters of mercury.) The artery wall is compressed 
and the flow of blood is shut off. Quickly close the screw clamp 
and remove the pump. Allow the air to escape gradually from the 
bag by slowly opening the screw clamp. The reappearance of the 
pulse may be detected by observing the pulsation of the mercury 
column. It is very faint at first, and it increases to a maximum 
throb when the pressure in the bag is the same as the pressure in 
the artery. When this maximum throb is reached, measure the 
difference in levels in millimeters. This is the systolic pressure. 
Make three determinations and average the readings. 

1. What is your systolic pressure in millimeters of mercury? 

2. Make a careful diagram of the apparatus. 

3. When the pulse first reappears, how does the pressure in 
the artery compare with the pressure in the rubber bag ? 

4. Would you expect the blood pressure at the feet to be 
greater or less than that at the head? Explain. 

5. When a person faints or feels faint, why should the head 
be placed low? 

6. If a man's blood pressure is one hundred and forty milli- 
meters of mercury, to what height would his heart pump a column 
of water? (Mercury is thirteen and six- tenths times as heavy as 
water.) 



88 LABORATORY PROJECTS IN PHYSICS 

7. How high is this in feet? (One foot equals three hundred 
and five millimeters.) 

8. What pressure is this in pounds per square inch? (Two 
and three-tenths feet of water column press one pound per square 
inch.) 

9. At each beat a man's heart forces eight cubic inches of 
blood into the arteries against a pressure of two and one-half 
pounds per square inch. How much work in foot-pounds is done 
by this man's heart at each beat? (Eight-twelfths of a foot 
times two and one-half pounds.) 

10. At the rate of sixty beats per minute, how many foot- 
pounds of work is done by this man's heart in twenty-four hours? 

11. How many feet vertically would the work of question 10 
lift a man of one hundred and fifty pounds weight ? A man could 
accomplish this work by two hours of steady mountain climbing. 
The heart does about one-fourth as much work as all other muscles 
combined. 

NOTE : A common method of detecting the return of the pulse 
when the pressure is gradually released from the bag is by means 
of a stethoscope placed on the artery above the elbow. This 
requires a quiet room for accurate results. Another method 
is by noting the return of the pulse felt at the wrist in the usual 
way. 

The technical name for the blood pressure apparatus is 
sphygmomanometer. In place of the U-tube and the mercury 
column a small dial-pressure-gauge is frequently used. In this 
type of instruments the changes in pressure produce changes 
upon a sensitive metal diaphragm which in turn operates the 
indicator on the dial. 



THE CAMERA A 



8 9 



38. THE CAMERA A 

Preliminary work: To study lens images as related to the opera- 
tion of a camera. 

. MATERIALS. 4X5 focusing camera with rapid rectilinear lens and plate- 
holder; pinhole camera; simple lens; cardboard screen; pinhole cardboard. 
(Part of the apparatus for this experiment must be obtained from the instructor.) 





FIG. 36. A focusing camera. 



QO LABORATORY PROJECTS IN PHYSICS 

The camera, like the human eye, and the projection lantern, 
requires three essential conditions for its operation, an j illumi- 
nated object, a lens, and a screen. An illuminated object, for ex- 
ample, a flame or a house, consists of an infinite number of points, 
each of which is a source of light radiation. When a lens is placed 
between an illuminated object and a screen, an image of the object 
may be produced upon the screen. Each point on the object 
sends some of its light against the whole face of the lens. The 
lens converges (focuses) this light to a corresponding point on the 
screen. An infinite number of such points produce the complete 
image of the object. 

Simple Lens Images. With a gas flame or candle flame as ob- 
ject, place a lens between the flame and a cardboard screen in 
such position that an image of the flame is projected upon the 
screen. The lens and screen may be fastened to the clamps of 
two ring stands. 

1. Replace the lens with a card having a pinhole in it. Ex- 
plain how a pinhole produces an image. Diagram it. Why is 
the image inverted? See Mann and Twiss. Look through the 
pinhole camera and observe the image of a building on the ground 
glass. 

2. Diagram a lens focusing parallel light rays. Show how 
a reading glass lens (convex lens) refracts the sun's rays in the 
case of burning a piece of paper. See Mann and Twiss. 

3. Diagram light rays diverging from a single point and strik- 
ing the face of a lens and being converged or focused to a point 
on the opposite side. See Mann and Twiss. 

4. Diagram light rays proceeding from two points on an ob- 
ject (top and bottom of a flame) through a lens to the screen. 
Draw the paths of three rays from each of the two points, one 
ray striking the lens near the upper edge, one passing through 
the center of the lens and one striking the lens near the lower edge. 



THE CAMERA A 91 

5. Place the object (flame), lens, and screen in such positions 
that the image of the flame on the screen is equal in size to the 
object. When the object is the same in size as the image, how 
does the distance between the lens and object compare with the 
distance between the lens and image? Diagram the situation. 

6. Can an image be made if only the central region of the 
lens is used? Place a card over the lens with a hole about a 
quarter of an inch in diameter. How does this affect the image? 

7. Place the object, lens, and screen in such positions that the 
object appears three times as large as the image. In this case how 
does the distance between lens and object compare with the dis- 
tance between lens and image? Diagram this situation. 

8. If the object is moved closer to the lens, how must the 
screen be moved to make a sharp image ? 

9. If both object and screen are moved farther away from the 
lens, how may the lens be moved to obtain a sharp image? 

10. In taking a picture with a focusing camera, which one of 
the three parts is ordinarily moved in focusing, object, lens, or 
screen ? 

11. In taking a picture with a camera, what must be done to 
obtain a larger image on the screen ? 

12. In taking a picture with a focusing camera, if the object 
is moved closer to the camera, how should the lens be moved 
to make the focus sharp? 



LABORATORY PROJECTS IN PHYSICS 



39. ELECTRIC MOTOR A 

Preliminary work: To study the construction and operation of an 

electric motor. 

MATERIALS. St. Louis motor ; two dry cells ; No. 24 wire ; thirty-five 
ampere battery ammeter. 




No. 2 



No. 3 



Motor; Bar Magnet Shunt Motor; Electro Series Motor; Electro 



Fields. 



Magnet Fields. Magnet Fields. 

FIG. 37. A simple electric motor. 



No. 4 
The Motor may be 
used as a generator. 



One form of simple electric motor consists of two electromag- 
nets one stationary and the other so arranged that it revolves in 



ELECTRIC MOTOR A 93 

the magnetic field of the stationary coil. A device known as a 
commutator reverses the direction of flow through the revolving 
coil each half turn. The principal parts of a motor are: field 
magnet, field coil, armature (revolving coil), commutator, and 
brushes. 

A. Motor Operated with Permanent Field Magnet. Remove 
the field coil attachment from the base board and lay it aside. 
Using the two permanent bar magnets for the field magnetism 
attach wires from one dry cell to the upper binding posts, causing 
the armature to rotate. 

1 . Name two of the essential parts of the motor through which 
the current passes before it reaches the armature coil. 

2. What causes the armature coil to become magnetized? 

3. When the current is reversed through an electromagnet what 
happens to its poles? 

4. For what part of a revolution does the current flow in one 
direction through this armature coil? 

5. How many times during each revolution are the poles of 
this armature reversed? 

6. State the law which applies to the attraction and repulsion 
of magnetic poles. 

7. What should happen with regard to the direction of current 
flow when the south pole of the armature comes nearest to the 
north pole of the field? 

8. What effect upon the direction of rotation of this motor 
is caused by reversing the field poles? 

9. Reverse the battery wires at the brush posts of the motor. 
What effect has this upon the direction of rotation? 

10. What effect upon the speed of the armature is produced by 
turning the brush frame out of its normal position? 

11. If the field poles are both north or both south (like poles), 
how does this affect the rotation of the armature? 



94 LABORATORY PROJECTS IN PHYSICS 

B. Motor Operated with Electromagnet for its Field. Push 
the permanent bar magnets aside and place the electromagnet 
coil in position to furnish the field magnetism. Connect wires 
so that current from two dry cells passes first through the 
armature coil and then through the field coil and back to the 
dry cells. This represents a series wound motor. 

12. Diagram a series wound motor. Observe the illustrations 
and refer to text on wiring of motors or generators. 

13. Connect a battery ammeter and measure the current which 
the pressure of two dry cells sends through the motor. 

14. Two dry cells in series have approximately three volts 
pressure. What is the resistance of this motor in ohms? While 
measuring the current for resistance do not let the armature 
rotate. Hold it. Apply Ohm's Law (Volts divided by ohms equal 
amperes). 

15. This motor would be ruined if attached directly to the 110- 
volt lines. With its resistance known, calculate by Ohm's Law 
how many amperes would pass through it if it were attached to 
the 1 10- volt line. 

1 6. Operate this motor with shunt wiring. Inquire of the 
instructor. Diagram a motor wired in shunt. See Black and 
Davis. Use diagram for shunt generator, omitting lamps. 



THE FIRELESS COOKER: INSULATORS 



95 



40. THE FIRELESS COOKER: INSULATORS 

To determine the quantity of heat that will escape in a given 
time from a fireless cooker, a thermos bottle, and an open 
vessel. 

MATERIALS. Fireless cooker (commercial type); gas burner; 4-quart 
aluminum saucepan ; thermos bottle ; copper quart measure ; 200 c.c. graduate ; 
Fahrenheit thermometer ; tin funnel. 



/nsu/ateo 1 cover. 

msr==sru 

Aluminum Linin 
Miners/ Woo/ 




FIG. 38. Sectional view of a fireless cooker. 

A. Fireless Cooker. Measure carefully three quarts of water 
and heat it in the cooker vessel until the temperature reaches 
200 F. Inclose this vessel in the fireless cooker, noting the time. 
Allow it to remain in the cooker for thirty minutes. Open and 
again note the temperature. 

B. Open Vessel. Measure carefully three quarts of water 
and heat it in an open vessel (saucepan) until the temperature 
reaches 200 F. Remove the vessel from the stove and place it 
on an asbestos mat, noting the time. Allow it to cool for thirty 
minutes and again note the temperature. 



9 6 



LABORATORY PROJECTS IN PHYSICS 



bber R/nc? 



C. The Thermos Bottle. Fill the thermos bottle with water 
heated to 200 F. Use a funnel. Insert the stopper and note the 
time. At the end of thirty minutes note the temperature and pour 

the water from the thermos 
bottle into some other vessel 
and allow it to cool. Then 
pour it into a glass graduate 
in order to find its volume 
in cubic centimeters. Cal- 
culate its weight in pounds. 
(One pound equals four hun- 
dred and fifty-four cubic 
centimeters.) (One quart 
weighs two and eight hun- 
dredths pounds.) 



Vacuum 

Thermos Patent_ 
/?einforcemen 



Absorber 




ffeavy G/ass 

Base 
""or/c Cushion 



FIG. 39. Sectional view of a thermos bottle. I - How much heat in 

B.T.U. above room tempera- 
ture was added to the water of each vessel (pounds times degrees 
rise above room temperature) ? 

2. How much heat escaped from the water in each vessel 
during the thirty minutes of cooling (pounds times degrees drop 
from two hundred)? 

3. In the case of each vessel what per cent of the heat added 
above room temperature was retained after thirty minutes of 
cooling ? 

4. Does a vessel filled with hot water lose heat at a more 
rapid rate than one filled with warm water? Explain. 

5. When the water in a vessel cools explain how the cooling 
may involve conduction, convection, and radiation. Define 
each. Refer to texts. 

6. If the room were very cold how would this affect the rate 
of cooling ? Explain. 

7. Make a sectional diagram showing the structure of the waUs 



THE FIRELESS COOKER: INSULATORS 97 

of a fireless cooker. See texts by Butler or Lynde or Carhart 
and Chute. 

8. Name some materials that might be used in the construction 
of the walls of a fireless cooker. 

9. Suggest three advantages of the fireless cooker in the cook- 
ing of meats and vegetables. Has it any disadvantages? 

10. In the thermos bottle, (a) what useful purpose does the 
vacuum serve? (b) What useful purpose does the mirrored sur- 
face serve? (c) Why does a thermos bottle have two mirrored 
surfaces? See Carhart and Chute. 

11. With respect to heat transfer how does a refrigerator or 
ice box differ in its operation from a fireless cooker? 

The common commercial forms of fireless cookers are simpler in 
construction than that shown in the accompanying illustration. 
As a rule the cheaper grades of cookers have very inexpensive 
packing of felt, paper or other insulating material. 

A home-made fireless cooker may be constructed by placing a 
galvanized iron pail in a wooden box and packing around it, on 
all sides, a three-inch layer of excelsior, straw or paper. This will 
serve as a more efficient insulator of heat than the ordinary com- 
mercial forms of cookers. 



9 8 



LABORATORY PROJECTS IN PHYSICS 



41. THE GAS STOVE BURNER 
Heating Water Cost and Efficiency. 

To determine the cost of heating a quart of water from 75 F. to the 
boiling point, 212, using, as fuel, illuminating gas. 

MATERIALS. Gas burner; gas meter; screw clamp; clock; copper 
quart measure ; four-quart saucepan ; Fahrenheit thermometer. 



Met s/cfe 



Out/et s/cfe 





Gaa stove 

FIG. 40. Connections for measuring the amount of gas :; quired to heat water. 

A . Heating by Gas Burner. Connect a piece of rubber tubing 
from the gas-cock to the side of the gas meter marked " inlet." 
Attach the burner to the other side of the meter. (Caution. 
Allow a quarter of a cubic foot of gas to flow through this meter before 
lighting it.) Place a screw clamp on the tube between the meter 
and the burner. Adjust the clamp by opening and closing so 
that exactly one cubic foot of gas flows through the meter in four 
minutes as indicated by the second hand of the clock. 

Measure carefully one quart of water and heat it in a four-quart 
saucepan to 75 F. Stir to insure a uniform temperature. When 
the temperature of the water reaches 75 F., record the reading of 
the gas meter. Place a cover on the vessel and allow the heating 



THE GAS STOVE BURNER 99 

to continue till the water begins to boil as indicated by a rapid 
evolution of steam bubbles (not air bubbles) from the bottom of 
the vessel. Readjust the screw clamp each minute to keep the meter 
hand in proper step with the second hand of the clock. Take a 
careful record of the amount of gas consumed in the heating opera- 
tion. 

1 . How many cubic feet of gas were consumed in the heating ? 

2. Calculate the cost at one dollar per thousand cubic feet. 

3. How many B.T.U. did the water receive (pounds of 
water times degrees rise) ? One quart weighs two and eight hun- 
dredths pounds. 

4. How much heat was generated by the amount of gas con- 
sumed (one cubic foot gives out six hundred B.T.U.) ? 

5. What per cent of the total heat generated by the burning of 
the gas entered the water in the vessel? This result represents 
the heating efficiency of the operation. 

B. Repeat the test without a cover on the vessel. 

6. What is the cost of heating with cover removed? 

7. What is the efficiency with cover removed? 

8. Make a table including the results of A and B with columns 
showing gas consumed, cost, and efficiency. 

C. The Gas Burner. This device is a form of Bunsen burner. 

9. Hold your hand over the air inlet and cause the flame to 
become yellow. Explain. 

10. If the air inlet is too large what happens to the flame? 
Some burners have an adjustable slide for controlling the mixture. 

11. If the flame is turned too high under a vessel of cold water 
a poisonous gas is sometimes given off. Explain. See-Bodgdori. 

12. Explain the fact that less gas is required to heat water if the 
vessel is covered. 

13. List at least three ways in which gas is often burned un- 
necessarily in the kitchen. 



100 



LABORATORY PROJECTS IN PHYSICS 



42. GASOLINE ENGINE A 
To operate a gas engine and explain its action 

MATERIALS. Gas engine ; ignition-bottle ; large glass jar ; rubber tube ; 
induction coil ; four dry cells ; telephone magneto with small lamp. 



\0/f cuf> 



,Connectiny rod 



Cylinder 
Mayneto 



fntake va/ve - 
Exhaust valve 



Crank 
Crank 3 ha ft 



F/y whee/s 




FIG. 41. A gasoline or gas engine. 

A. The Explosive Mixture. Fill the ignition-bottle with watei 
and invert in the glass jar of water. Attach the rubber tube to 
a gas cock. Collect a half bottle of gas by displacement over 
water. Remove the bottle allowing air to enter forming a mixture 
of half gas and half air. Hold your hand over the end of the bottle 
and invert a few times to mix the air and gas. Remove your 
hand and bring a lighted match to the mouth of the bottle. Does 
the mixture burn? 

i. Does a bottle of pure illuminating gas burn more or less 
readily than half air and half gas? 



. GASOLINE ENGINE A IOI 

2. Vary the proportions of the mixture and determine from 
the report of the explosion approximately what proportions by 
volume of air and gas give the most effective explosion. Which 
gives the better explosive mixture, one-fourth gas or one-fifth 
gas? 

3. What is meant by the statements that the mixture in an 
engine is " too rich " or " too lean "? 

B. Ignition. The magneto and the induction coil. The 
explosion in gas engines is caused by a spark from a magneto 
(electric generator) or from an induction coil operated by dry cells. 
Operate a magneto generator, causing it to light a small lamp. 
(Caution. An induction coil is dangerous. Do not touch the 
secondary terminals after attaching the lattery to the primary.} 
Attach a wire from one terminal of the secondary coil to within a 
quarter inch of the other. This will form the spark-gap. Connect 
one terminal of the battery of four dry cells to one terminal of the 
primary. Touch the other battery terminal to the primary ter- 
minal of the coil. The vibrator changes a continuous battery 
current to an intermittent current. An intermittent current in the 
primary causes a very high voltage current to be induced in the 
secondary. This high voltage current produces the spark for the 
ignition. (Caution. To avoid the possibility of an accidental shock 
from the secondary terminals always disconnect the dry cells from an 
induction coil while working with the secondary circuit.) Attach wires 
from the secondary terminals to a spark plug and operate it. 
Mount the spark plug in a ring-stand clamp. 

4. Diagram the apparatus showing induction coil, four dry 
cells, and spark plug with proper wiring. See Experiment 91. 

The type of induction coil used in operating a gas engine is 
commonly a simple spark coil. It consists of a simple coil of 
many turns of wire with a soft iron core at the center. This small 
type of coil gives a hot spark when the contact is broken. The 
igniter mechanism on the side of the cylinder operates the " make 



102 LABORATORY PROJECTS IN PHYSICS 

and break " furnishing a hot spark inside at the proper time. 
This is called a " make and break " system of ignition. When 
a spark plug is used as in an automobile it is known as a "jump 
spark" system. The vibrator type of induction coil furnishes a 
jump spark. The electric current for ignition may be produced by 
a magneto generator which is operated by the engine. As a source 
of ignition current the magneto is preferable to dry cells since dry 
cells will soon run down and require replacing. 

C. The Engine. Before starting fill the cylinder hopper with 
water. Oil the cylinder and bearings. This engine may be operated 
with illuminating gas instead of gasoline. The air and illuminating 
gas are mixed at the mixing valve. Ask the instructor to start 
the engine. Keep a safe distance from moving wheels. Observe 
its operation. Locate the following parts, mixing- valve, cylinder, 
piston, intake valve, exhaust valve, crankshaft, cam, and cam 
rod. 

5. Make four diagrams representing the four strokes (half 
revolutions of a four-stroke engine). See Millikan, Gale and 
Pyle or Black and Davis. 

6. What causes the mixture to enter the cylinder? 

7. What adjustment must be made at the mixing- valve to get 
effective working conditions? 



HEATING A ROOM COST A 103 

43. HEATING A ROOM COST A 

To determine the cost of heating an average room by (a) gas 
stove, (b) basement furnace, (c) electric heater. 

On a cold day a room of average construction, exposure, and 
ventilation will require approximately five thousand B.T.U. per 
hour for each thousand cubic feet of room space. A room 
10 X 15 X 10 feet high contains fifteen hundred cubic feet. It 
will therefore require seven thousand five hundred B.T.U. per hour. 

Determine the cost of heating this room per hour by each of the 
following methods : 

A. Heating by Gas Stove (without flue). 

1. One cubic foot of gas supplies six hundred B.T.U. How 
many cubic feet of gas will be required to heat this room per hour ? 

2. What will be the cost per hour at one dollar per thousand 
cubic feet? 

B. Heating with a Basement Furnace (steam, hot-water, or 
hot-air). 

3. One pound of coal of average quality furnishes thirteen 
thousand B.T.U. when burned in a furnace or stove. How many 
pounds of coal will be required to heat this room per hour if only 
sixty per cent of the furnace heat reaches the radiators ? 

4. What becomes of the other forty per cent of the heat of the 
coal? 

5. What will be the cost per hour at ten dollars per ton? 

6. Calculate the amount of coal required to heat six rooms for 
one cold day of twenty-four hours if for eight hours during the 
night only one- third heat is required. 

7. Calculate the amount of coal required for the heating period 
of two hundred days if the average heat for each of the two hun- 
dred days is three-sevenths of that required for a cold day. 



104 LABORATORY PROJECTS IN PHYSICS 

C. Heating with an Electric Heater. 

8. One kilowatt-hour generates three thousand four hundred 
B.T.U. How many kilowatt-hours of energy will be required 
to heat this room for one hour? 

9. What will be the cost per hour at eight cents per kilowatt- 
hour? 

10. Is any heat lost in the case of the electric current ? 

D. Summary. As a summary arrange the results of the three 
calculations in a table with columns showing the following data : 
(a) cost of heating a six-room house per hour ; (b) cost of heating 
a six-room house per day, considering that for eight hours during 
the night only one-third as much heat is required as during the day ; 
(c) cost of heating a six-room house for a year, considering that the 
average heat for two hundred days' heating is three-sevenths of 
that required for two hundred cold days. 

E. Reference Work : General Science, Barber. 

11. List the heat value per pound of the following: carbon, 
hydrogen, oak wood, pine wood, bituminous coal, anthracite coal, 
petroleum. 

12. What was a Roman hypocaust ? 

13. Contrast advantages of steam and hot- water heating 
systems. 

14. Diagram a ball and lever safety valve. 

15. As the pressure rises in a steam boiler what is the effect 
upon the boiling point? 



HEATING A ROOM COST B 105 

44. HEATING A ROOM COST B 

To determine the cost of heating an average room by (a) coal 
stove, (6) wood stove, (c) open fireplace. 

On a cold day a room of average construction, exposure, and 
ventilation will require approximately five thousand B.T.U. per 
hour for each thousand cubic feet of room space. A room 
10 X 15 X 10 contains fifteen hundred cubic feet. It will therefore 
require seven thousand five hundred B.T.U. per hour. 

Determine the cost of heating this room per hour by each of the 
following methods : 

A. Heating with a Coal Stove. 

1. One pound of coal of average quality furnishes thirteen 
thousand B.T.U. when burned in a stove. How many pounds of 
coal will be required to heat this room per hour if seventy per cent 
of the heat reaches the room? 

2. What will be the cost of heating the room for one hour 
at ten dollars per ton? 

Stoves provide one of the most economical means of heating 
because they are located in the room and usually not many rooms 
are supplied. Houses are often heated in this way and may 
require only three to five tons of coal for the entire winter, while 
an average house with a steam or hot-water furnace may require 
fifteen to twenty-five tons. 

3. Explain why a stove in a room furnishes a higher percentage 
of the heat to the room than a furnace in the basement ? 

4. Calculate the amount of coal required to heat two rooms 
for one cold day of twenty-four hours if for eight hours during the 
night only one-third heat is required. 

5. Calculate the amount of coal required to heat two rooms for 
the heating season of two hundred days if the average heat is 
three-sevenths of that required for cold days. 



106 LABORATORY PROJECTS IN PHYSICS 

B. Heating with a Wood Stove. 

6. A pound of dry wood generates eight thousand B.T.U. 
If a wood stove is seventy-five per cent efficient how many pounds 
of wood will be required to heat this room for one hour? 

7. What will be the cost per hour at eight dollars per cord? 
A cord of wood weighs two tons. 

8. At these rates how does heat from a wood stove compare 
in price with heat from a coal stove ? 

9. Mention advantages and disadvantages of wood stoves 
and coal stoves aside from cost of fuel. 

C. Heating by Open Fireplace. 

10. An open fireplace is about thirty per cent efficient. Using 
data under B how many pounds of wood would be required to heat 
the room for one hour? 

11. What would be the cost per hour? 

12. Which one of the three methods of heat transfer is in- 
volved chiefly in the operation of a fireplace? Refer to texts. 

D. Summary. Make a summary of the results of the three 
calculations in the form of a table with columns showing the follow- 
ing data : (a) cost of heating a six-room house per hour ; (b) cost 
of heating a six-room house per day, considering that for eight 
hours during the night only one-third as much heat is required as 
during the day ; (c) cost of heating a six-room house for a year, 
considering that the average heat for two hundred days' heating is 
three-sevenths of that required for two hundred cold days. 



HOUSE GAS SUPPLY CITY GAS 



107 



45. HOUSE GAS SUPPLY CITY GAS 
To study the operation of household gas appliances. 

MATERIALS. Gas meter; rubber tubing; laboratory Bunsen burner; 
gas stove burner ; gas iron ; open flame gas lamp. 



ry y \ 

F^l 




Gas Stove 



Gas Range 

FIG. 42. Typical gas appliances. 



Gas Heater 



A. Attaching a Gas Meter. Connect a tube from a gas cock 
to the inlet side of the meter. To the outlet side of the meter 
attach a laboratory Bunsen burner. (Caution. Allow a quarter of 
a cubic foot of gas to flow through the meter before lighting it.) Note 
that the Bunsen burner is a device for permitting air to mix with 



108 LABORATORY PROJECTS IN PHYSICS 

the gas before the gas reaches the flame. It is provided with 
adjustments which vary the proportion of gas and air. 

1. Diagram a Bunsen burner and briefly explain its construc- 
tion. See General Science, Hodgdon. 

2. Adjust the burner so that it gives a colorless or bluish 
flame. Explain why it is colorless. See General Science, Hodg- 
don. 

3. Adjust the burner so that the flame is yellow. Explain 
why it is yellow. 

4. Adjust the burner so that the flame smokes. Explain. 

5. Adjust the burner so that the flame " strikes back." Ex- 
plain. (Caution. Do not permit gas to continue burning at the 
bottom. The gas generated is poisonous.) 

B. The Gas Meter. A house gas meter consists of a sheet 
metal box with a partition dividing it into halves. Each half 
is divided into two compartments by a diaphragm, making four 
compartments in all. Gas, in flowing through the meter, moves 
the diaphragms which operate the dials and register the amount of 
gas used. Gas alternately enters and leaves the compartments. 

6. Make a simple diagram showing the four compartments, 
the diaphragms; and the valves of a gas meter. See Household 
Physics, Butler ; or General Science, Barber. 

7. Make a diagram of the dials and state the reading in cubic 
feet registered by one of the laboratory gas meters. Have your 
reading approved by the instructor. 

C. Gas Stoves and Ranges. The gas stove is a modification 
of the Bunsen burner. Stove burners are often equipped with an 
adjustable air vent. 

8. Hold your hand over the air inlet of the stove burner. 
Explain the effect upon the flame. 

9. Diagram a star-shaped range burner showing adjustable 






HOUSE GAS SUPPLY 109 

air vent. What is the reason for this shape? See Mechanics of 
the Household, Keene. 

10. What are the two common types of burners on gas stoves? 
See General Science, Hodgdon. 

11. State the main points in adjusting a gas burner. See 
General Science, Hodgdon. 

12. When a gas burner is opened wide, especially if the flame is 
cooled by a kettle of cold water, it sometimes gives off poisonous 
fumes. Explain. See General Science, Hodgdon. 

D. The Gas Iron. Attach a gas iron to the meter and heat it. 
Adjust the flame till you consider that enough heat is generated for 
continuous ironing. 

13. Let the gas flow at the ironing rate for ten minutes and note 
the amount of gas consumed. Calculate the cost of operating 
the iron per hour at one dollar per thousand cubic feet. 

An electric iron costs about five cents per hour for current. 

E. The Gas Lamp. Attach an open flame burner by means 
of a rubber tube with screw clamp. With the screw clamp adjust 
the burner. 

14. Operate the open flame burner for ten minutes and calcu- 
late the cost per hour. 

15. Explain the operation of a Welsbach mantle. See General 
Science, Hodgdon. 



110 



LABORATORY PROJECTS IN PHYSICS 



46. HOUSE WATER SUPPLY 

To attach a supply pipe including stopcock, meter, and faucet to 
the water line and study their operation. 

MATERIALS. Piping ; stopcock ; water meter ; two feet of flexible hose ; 
screw faucet; compression-faucet; faucet washers; hose washers; fixtures; 
gallon measure ; wrench ; screw driver. 

A. Testing the Meter. (Caution. Do not attach this meter 
to a hot-water faucet as one of the moving parts is made of hard rubber 



S/nk Faucet 



fiubber ffose 




Water Meter 



~^~*\ f Ga//on Measure 

FIG. 43. Apparatus for the study of house water supply. . 

which would be injured by hot water.) Attach the meter with piping, 
stopcock, and faucet to the laboratory faucet by means of the 
flexible rubber hose. Note. Place hose washers in the ends of 
the flexible hose to prevent leakage. When attachments are all 






HOUSE WATER SUPPLY III 

made tight allow water to flow through noting that the indicator 
on meter dial registers the number of cubic feet of water used. 

1. With the gallon and quart measures determine carefully 
how many quarts of water flow through while the meter registers 
one cubic foot. (Two hundred and thirty-one cubic inches equal 
one gallon.) How does the dial reading compare with your actual 
measurement ? 

2. What is the purpose of the stopcock on the house water 
supply line ? 

3. If for any reason the water pipes in the house burst, what 
would you do in the emergency to prevent a flood ? 

4. Why is it necessary to lay water pipes deeper in the ground 
than gas pipes? 

5. Make a sketch of the dials of a water meter and state the 
reading. See General Science, Hodgdon. For sectional view of 
water meter see Hodgdon, and General Science, Barber. 

B. Faucets Operation and Repair. Shut the water off a-t 
the stop-cock. Open the faucet with a wrench by unscrewing the 
top. Remove the screw and note that there are two washers to 
prevent leakage, one at the top of the screw and one at the bottom. 

6. Diagram a screw faucet. See Butler's Household Physics. 

7. Diagram a compression faucet. 

8. In the screw faucet when does the lower washer function? 
When does the upper one function? 

9. If a screw faucet leaks when it is turned off how might this 
trouble be remedied ? 

10. If a screw faucet leaks at the handle when it is turned on, 
how might this trouble be remedied? 

C. Closet Tanks. The closet tank serves as a reservoir for 
flushing the closet. The amount of water is controlled by an 
automatic float valve which rises when the tank gets full and shuts 
off the in-flowing water. It also provides for an outlet attachment 



112 LABORATORY PROJECTS IN PHYSICS 

which remains open till the tank is completely emptied and then 
closes automatically. 

11. Diagram the old form of closet tank. See Butler. 

12. Diagram two common types of closet tanks in use at the 
present time. See General Science, Hodgdon. 

13. Explain the action of the siphon type of tank. 

47. THE DEW POINT 

To determine the dew point (temperature) of the air in the labora- 
tory at a particular time. 

MATERIALS. Polished nickel-plated beaker, capacity about five hundred 
c.c. ; Fahrenheit thermometer ; ice ; pan for ice. 

A. Water Vapor in the Air. Water from rivers, lakes, the 
ocean, etc., is continually evaporating into the air. When the 
air gets filled with moisture and is chilled by a cold wind in the 
upper atmosphere, fogs form into clouds and drops of water fall 
down as rain. Air takes up moisture in the same way that water 
dissolves certain salts. It is very important to note the fact that 
warm air can hold (dissolve) many times as much water as cold 
air. When saturated air is chilled it may result in a fog. If the 
earth cools at night and chills the air it may result in the formation 
of dew. If saturated air in the upper atmosphere is chilled by a 
cold air current it may result in clouds (fog), snow, or rain. The 
temperature at which any given air begins to give out moisture is 
called the dew point for that particular air. The dew point of 
the air in the laboratory may be found by placing water in a metal 
cup and gradually cooling it. The cold cup then chills the air 
surrounding it and dew begins to form on the outside of the cup. 

B. Determination of the Dew Point of the Air in the Room. 

Place in the cup two hundred cubic centimeters of water at about 
the temperature of the room. Stand the thermometer in the water 



THE DEW POINT 113 

and slowly cool it by dropping in pieces of ice about the size of a 
nickel. Cool the water carefully at the rate of four degrees per 
minute. Stir the ice and water constantly in order to get a correct 
result. Observe the polished surface of the cup for the first appear- 
ance of moisture as indicated by your finger leaving a path when 
rubbed over the cup. Do not breathe against the cold cup. 
When the first dew is noticed read the temperature of the ther- 
mometer in the water. (If the indoor air is very dry, as it often is in 
winter, it may be necessary to add salt to the ice.) This temper- 
ature should be the approximate dew point. It is too low because 
you really cooled the water a few degrees below the dew point before 
the dew was observed. Make at least three determinations and 
see if they agree. Correct your result by adding two degrees since 
you did not actually see the moisture till after it first appeared. 
Test the correctness of this result. If moisture continues to form 
raise the temperature two degrees above it by adding a little hot 
water and see if the moisture disappears. A preferable method 
is as follows : When the first dew is observed take the temperature. 
Then heat the water at the same rate as it was cooled, by adding 
small quantities of hot water, and note the temperature at which 
the dew disappears. The dew point should be the average of 
these two temperatures. 

1. With respect to dew point explain what causes drops of 
water to form on a pitcher and frost to form on the window pane. 

2. What makes one's breath visible on a cold day? 

3. What is meant by a good drying day for laundry purposes ? 

4. How does the air in a refrigerator lose its moisture? See 
General Science, Barber. 

5. Explain the formation of clouds and fogs. See Weather, 
Jameson, or General Science, Barber. 

6. Explain the formation of rain and snow. 



114 



LABORATORY PROJECTS IN PHYSICS 



48. THE JACK-SCREW 

MATERIALS. Jack-screw; two so-lb. iron weights; yardstick; small 
spring balance. 



5O/b. test weight 



i /8 /nches 




FIG. 44. Lifting a fifty-pound weight by means of a jack-screw. 

Jack-screws are often used in lifting a building from its founda- 
tion. A comparatively small force exerted through a long distance 
in turning the handle exerts an enormous upward force through a 
small distance. In one revolution of the jack-screw the screw is 
lifted the distance between two threads of the screw. 

A. Operating a Jack Screw. Put a fifty-pound weight on the 
top of the jack-screw. Place the iron rod in the opening. At a 



THE JACK-SCREW 

point eighteen inches from the center of the jack-screw pull the 
handle with a small spring balance. 

1. How far in feet does a point on the handle eighteen inches 
from the center of -the screw move in lifting the screw the distance 
between two threads (circumference of the circle) ? 

2. What is the amount of this force in pounds, in lifting fifty 
pounds ? 

3. What is the " work in " in foot pounds done per revolution 
(pounds times circumference)? 

4. If the distance between two threads is five-sixteenths of an 
inch, what is the "work out" in foot pounds done per revolution? 

5. What is the efficiency (" work out " divided by "work in ") ? 

6. In the operation of the jack-screw what causes the " work 
out " to be so much less than the " work in "? 

7. Suggest a means of increasing the efficiency of this device. 

8. When work or energy seems to disappear as a result of 
friction into what is it usually transformed? 

B. Efficiency with Two Fifty-Pound Weights. With the in- 
structor's assistance place two fifty-pound weights on the jack- 
screw, one above the other. Place them in position very carefully 
so that they do not fall off. Handle cautiously to avoid injury and 
remove the weights as soon as the measurements are made. 

9. Determine the efficiency in lifting one hundred pounds. 

10. A screw is a modification of an inclined plane. See Hoadley. 
The slope of a hill is one thousand feet in length. If the hill is 
fifty feet in altitude (vertical distance between the levels of the top 
and bottom) how much work is done when a one-ton wagon is 
raised a vertical distance of fifty feet ? If in doing this a horse 
pulls the wagon with a force of one hundred and twenty pounds 
along the slope (one thousand feet) what is the "work in"? 

11. Calculate the efficiency in problem 10. 

12. What are some of the causes tending to reduce the efficiency 
below one hundred per cent in problem 10? 



u6 



LABORATORY PROJECTS IN PHYSICS 



49. THE KEROSENE STOVE 
Heating Water Cost and Efficiency. 

To determine the cost of heating a quart of water from 75 F. 
to the boiling point, 212, using, as fuel, kerosene. 

MATERIALS. Kerosene stove (single burner Perfection stove) ; can of 
kerosene ; copper quart measure ; 200 c.c. graduate for kerosene ; tin funnel ; 
tin pan, eight-inch diameter, for pouring kerosene from the stove ; four-quart 
saucepan or kettle ; Fahrenheit thermometer. 



Attvayi- keep 
\ space /i ere 




To t/'/t the 
F/ame Spreader 
raise this Lifter 



FIG. 45. Kerosene stove, wick type, showing burner and chimney parts. 

A. Heating by Kerosene Stove. Examine the stove tank 
carefully before you begin work to be sure that it is entirely empty. 
The instructor will give you directions in regard to emptying the 
tank. Using the funnel and 200 c.c. glass graduate, carefully 
place 300 c.c. of kerosene in the tank of the stove. (Caution. 
Make measurements accurately and avoid spilling a single drop. 



THE KEROSENE STOVE 

Drain the graduate thoroughly when pouring into the stove. Also 
drain the stove thoroughly when pouring into the graduate.) Before 
proceeding further with the experiment, test your ability to make 
these measurements by pouring the kerosene out again measuring 
it with the glass graduate and see if you can get out the same 
quantity of kerosene which you have put in. Have this procedure 
approved by the instructor. Again measure carefully and pour 
300 c.c. of kerosene into the tank of the stove. 

Measure carefully one quart of water and place it in the sauce- 
pan with cover and heat it on a gas burner to 75 F. Transfer the 
saucepan to the kerosene stove and light the burner. Have the 
stove inspected by the instructor at this point and he will advise 
you regarding the proper size of flame. It should be turned up 
so that the yellow tips of flame are visible above the blue flame. 
Heat the water to the boiling point (212 F., or evolution of steam 
bubbles) and extinguish the flame. Carefully pour out all of the 
remaining kerosene and measure it in cubic centimeters. Subtract 
from original amount. 

1. Record the number of cubic centimeters of kerosene con- 
sumed. Reduce to pounds. (Five hundred and sixty-seven c.c. 
of kerosene weigh one pound.) 

2. Calculate the cost of the fuel consumed at fifteen cents per 
gallon. (One gallon equals three thousand seven hundred and 
eighty-five c.c.) 

3. How many B.T.U. did the water receive? (Pounds of 
water times degrees rise. One quart of water weighs two and 
eight-hundredths pounds.) 

4. How much heat was generated by the amount of kerosene 
consumed? (One pound of kerosene generates twenty thousand 
B.T.U.) 

5. What per cent of the total heat generated by the burning 
of the kerosene entered the water in the vessel ? This result repre- 
sents the heating efficiency of the operation. 



Il8 LABORATORY PROJECTS IN PHYSICS 

B. The Kerosene Stove. This stove is similar in operation to a 
kerosene lamp. 

6. Explain how a large supply of oxygen reaches the flame. 

7. What is the function of the tall chimney? Why would a 
shorter chimney not do as well ? 

8. How does making the tank of flat shape and placing the 
burner as low as possible, reduce smoking and odor in a wick stove ? 

50. LEVERS AND SCALES 
To study levers and scales. 

MATERIALS. Two fifty-pound iron test weights ; five-foot iron crowbar 
(pinch point type) ; thirty-pound spring balance ; three-sided file for fulcrum ; 
laboratory beam balance ; steelyard ; platform scales ; wooden box eight inches 
on each side. 

Ca/cu/ate 
I downward force 
Crow-bar \i exerted here 









^ 


^V//e . 50/bs. 
F/oor 






Wooden 
Box 


1 ' 





FIG. 46. Lever with fulcrum located between the ends. 

A. The Crowbar. Place the file on the box. With this file 
as a fulcrum balance the crowbar on it. Mark the point on which 
the bar balances with a pencil or a piece of chalk. Use this point 
on the bar for the fulcrum. 

i. With a rope over the handle of one of the fifty-pound weights 
hang the weight on the bar at a point twenty inches from the 
fulcrum. Calculate the weight needed on the opposite end of the 
bar to balance the fifty-pound weight. Apply the lever law, 
weight times arm length on one side equals weight times arm 
length on the other side. (Power times power arm equals weight 
times weight arm.) 



LEVER AND SCALES 



2. With the fifty-pound weight in the same position as before, 
push downward at a point on the opposite side thirty inches from 
the fulcrum. Calculate the force in pounds required to balance 
the fifty-pound weight in this case. 

3. With the fifty-pound weight suspended from a point ten inches 
from the fulcrum, push downward on the opposite side at a point 
thirty inches from the fulcrum. Calculate the force required for a 
condition of balance in this case. 

4. Make diagrams of the three types of levers. How would you 
characterize each? Give two examples of each type. Refer to 
texts. 

t Student J5 
/ifts here. 



Wooden 
Box 



Crow-bar 



io /bs. 



50 /b. 



FIG. 47. Lever with fulcrum at one end. 

B. Lever with Fulcrum at the End. Place the sharp end of the 
bar on the file as a fulcrum. Let your associate hold the other end 
of the bar. Suspend the fifty-pound weight by means of its rope 
at a point twelve inches from the fulcrum. 

5. Applying the lever law, calculate the lifting force required 
at the end of the bar to support the fifty-pound weight located 
twelve inches from the fulcrum. (NOTE. Measure both lever 
arms from the fulcrum.) 

6. Hold the end of the bar with a thirty-pound spring balance. 
Note the reading of the balance with weight on. Then remove 
the weight and find how much of this downward force is caused 



120 LABORATORY PROJECTS IN PHYSICS 

by the weight of the bar itself. Subtract this amount from the 
previous reading. How does this result compare with the calcu- 
lated force in No. 5 ? 

7. Place the file on the floor and place the sharp end of the bar 
on it. Let your associate stand on the bar at a point eight inches 
from the fulcrum. Raise the other end of the bar with the thirty- 
pound balance. Ask a third person to note accurately the reading 
on the spring balance. Deduct for the weight of the bar and 
calculate your associate's weight. (Place the center of the heel 
on the proper point of the bar when the reading is made to get a 
more accurate result.) 

8. Diagram the apparatus used in problem seven. 

C. The Steelyard. Hang the steelyard on the laboratory 
pulley hook or some other convenient place. Place the fifty- 
pound weight on the proper hook and find its weight according to 
the steelyard. 

9. What weight does the steelyard register for the fifty-pound 
weight? (Move the scale weight toward the hook till it just 
barely begins to rise.) Because of inaccuracy the use of steel- 
yards for weighing is illegal in many states. 

10. Would you judge a steelyard to be more accurate on the 
light weight side, or on the heavy weight side? Explain. Weigh 
some object on the light weight side. (Change the hooks.) 

D. Balances. Examine an equal arm balance (platform type). 
See Barber's General Science. 

1 1 . Explain the purpose of the lower mechanism of a laboratory 
equal arm balance of the platform type. 

12. Remove the platform from the laboratory platform scales 
and examine the levers. Diagram the levers in a hay scales, 
marking all fulcrums with the letter F. See Millikan, Gale, and 
Pyle, or Hoadley. 






THE MICROSCOPE SIMPLE AND COMPOUND 121 

51. THE MICROSCOPE SIMPLE AND COMPOUND 

To construct a compound microscope and study its optical 

principles. 

MATERIALS. Ring stand ; two adjustable clamps ; small double convex 
lens of short focal length; reading glass lens; laboratory compound micro- 
scope. (Part of the apparatus for this experiment must be obtained from the 
instructor.) 

A. Lens Images. The compound microscope and the astro- 
nomical telescope are similar in principle in that both consist 
essentially of two lenses. In both instruments, the object produces 
an image by means of the objective lens. The eye-piece then 
magnifies this image. 

(NOTE. Handle lenses carefully and avoid scratching the sur- 
face of the glass. In making measurements, measure approxi- 
mately from the center of the lens.) 

1. Make a preliminary diagram of the image of a gas flame as 
it is produced on a cardboard screen by a simple convex lens, 
including object, lens, and image. See Mann and Twiss. Have 
this drawing approved. 

2. Diagram the human eye as an optical instrument. See 
Hoadley. 

3. Make a diagram showing how a convex lens magnifies an 
object. Include object, lens, eye and light rays. See Carhart 
and Chute, Black and Davis, Hoadley or Millikan, Gale, and Pyle. 

4. Measure approximately the focal length of each lens by hold- 
ing it in the path of parallel rays (rays from the sun). Focal 
length is the distance between the center of the lens and the point 
of sharp focus for parallel rays. Measure approximately from the 
outer edge of the lens. If you cannot get sunlight measure the 
distance from the lens of the image of a distant tree or pole. 

B, The Compound Microscope. With the clamp and ring 
stand place the lens of short focal length one and three quarters 



122 



LABORATORY PROJECTS IN PHYSICS 



inches from a book on the table. The second lens should be 
located approximately ten inches above the first. Observe a small 
letter on this page through the lenses. 




II 



I 



Ofyecftve 
tens 



p 


\ 




// ' ^ 


\ 


\ 




\\ 


\ 


,<-^ 


\ 


/ Lenses 


' !' 




, / 


.'! I 




l \ 


y*? 




\\ 


i * ' 
* i * 




\\ 


5 1 ' < 




\\ 


i*'i 
I >i i 




\\ 


< t 1 
1 n i 




\\ 


jf'j 




\\ 
\\ 


LM> 


y 


\\ 


j'j: 




"^ -^p6/ec//Ve\ 
/Lenses * 


ji! 


/ 


\ 


K 


KJ 


" / ^ / 



\ \ \ 
\ \ \ 



FIG. 48. Two simple lenses used as 
a compound microscope. 



FIG. 49. Lens arrangement in a high 
power microscope. See Fig. 50. 



5. Is the image produced by a compound microscope erect or 
inverted ? 

6. Diagram light rays passing through the two lenses of a com- 
pound microscope, showing how the first lens produces an image 
and the second lens magnifies that image. Indicate by dotted 
lines the points from which the rays appear to come as they enter 
the eye. 



THE MICROSCOPE SIMPLE AND COMPOUND 



I2 3 



V / 

VV 
/V\ 



/IT? 




< \\ 




' I/ i \ 




I* s 


1 


fed 


\ 


J * 


b\ 


(' 


, \ 


il M 


v 




x \ 


1 1 M 


\\ 


n !' 


\\ 


i .' 


\\ 


i i ' 
i 1 1 


\\ 


i ' ' 


\\ 


h ," 


\\ 


i . ' i 


\ 


i i 


\\ 


1 '' 


v\ 


1 !' 


h 


'. ' 


\\ 


!.; 


\\ 


1ft 


\\ 
^f^ \\ 


!(i > 


^x^/ftl \\ 


jTT i'i'Tt2 


///\] \\ 


3 el P 


.Jy ^^^ 




for 

/ Il/uminating the 
'^^ / Object at O. 



FIG. 50. A compound microscope showing the system of lenses. 



124 LABORATORY PROJECTS IN PHYSICS 

7. With respect to the size of the image formed on the retina 
of the eye, what effect should be produced in your improvised 
microscope by using an. eyepiece of shorter focal length ? 

8. How does enlarging an image affect its brightness? This 
is one reason why objects cannot be enlarged indefinitely. 

C. The High-Power Microscope. Examine a laboratory high- 
power compound microscope. (Caution. Do not remove any of 
the lenses without the assistance of an instructor. The objective and 
the eyepiece are composed of expensive compound lenses, very delicately 
adjusted. Do not touch the surfaces of these lenses with your fingers 
or any other object.} 

For high-power work the eyepiece unit and the objective unit 
consist of a combination of lenses, to produce more nearly perfect 
images. Simple lenses have three common defects, (a) spherical 
aberration or imperfect focus, (b) chromatic aberration or color 
fringes due to refraction and dispersion, (c) their images are not 
rectilinear, that is, they do not make straight lines on the object 
appear straight. 

9. What is an achromatic lens? See Hoadley. 

10. What is the purpose of the reflecting mirror at the base of 
a compound microscope? 

D. Reference Work. 

a. The Wonder Book of Light Houston. 

11. Upon what two conditions does the magnifying power of a 
simple lens depend ? 

12. How may the magnifying power of a lens be calculated 
approximately if the length of its principal focus (focal length) is 
known ? 

b. College Physics Kimball. 

13. What is an immersion lens ? 

14. Diagram the objective of a compound microscope. 

15. What focal length is common in a high-power objective? 



THE OPTICAL DISK 



125 



52. THE OPTICAL DISK 
To study reflection, refraction, and dispersion of light. 

MATERIALS. Optical disk with set of attachments. (This apparatus 
must be obtained from the instructor.) 




FIG. 51. Arrangement of apparatus for demonstrating reflection, refraction, and 
dispersion of light. 

This experiment requires sunlight. (Caution. Handle the 
glass parts of this apparatus with extreme care. The screws for 



126 LABORATORY PROJECTS IN PHYSICS 

fastening them to the disk should be provided with heavy leather or 
hard rubber washers. Fasten the glass parts firmly to prevent their 
Jailing off.) 

Place the optical disk in the path of the direct rays of the sun, 
letting the light shine through one or more narrow slots producing 
the paths of isolated light rays, across the face of the disk. With 
these rays it is possible to illustrate a great variety of the phenom- 
ena of reflection, refraction and dispersion of light. The work 
involves placing a sheet of paper behind the lenses, etc., and in- 
dicating by proper lines on the paper the position and direction of 
light rays with respect to the outline of the lens or other object. 
First, place the sheet of paper against the face of the disk and then 
place the glass in position against the paper. Push the screws 
through the paper into the proper sockets and fasten the glass 
firmly. Draw the outline of the glass on the paper. 

Demonstrate and diagram the following cases : 

1. A light ray as it is reflected from a plane mirror. Diagram, 
also, the reflection of a series of parallel rays. State the Law of 
Reflection. Refer to texts. 

2. A number of parallel rays reflected from a concave surface. 

3. A number of parallel rays reflected from a convex sur- 
face. 

4. A ray of light passing through a prism, showing both re- 
fraction and dispersion. Indicate by lines the blue ray on one side 
of the refracted beam and the red ray on the other. Is red light 
refracted more or less than blue light ? Which represents the more 
rapid vibration rates, red or blue? See Mann and Twiss, Color 
and Wave Length. A rapid vibration causes a short wave length. 
Is light ordinarily refracted toward the thin side or toward the thick 
side of a prism ? 

5. A series of parallel rays refracted in passing through a con- 
vex lens. Measure the focal distance of this lens. Name two 
conditions upon which the focal distance of a lens depends. Re- 
fer to texts. 



THE PRESSURE COOKER 127 

6. A series of parallel rays refracted in passing through a con- 
cave lens. 

7. A ray in passing through a thick piece of glass with parallel 
sides. Set the glass so that the ray strikes the surface of the 
glass obliquely. 

8. A ray in passing through a thick piece of glass with parallel 
sides. Set the glass so that the ray strikes perpendicular to the 
surface. Is there any refraction in this case? 

9. A ray striking the center of the flat side (center of curvature) 
of the semicircular glass with its center of curvature placed on the 
center of the optical disk. Adjust the angle of incidence so that 
part of this ray is reflected and part refracted. 



53. THE PRESSURE COOKER 
To study the operation of a pressure cooker. 

MATERIALS. One-burner gas stove ; pressure cooker, with thermometer 
attachment. 

(Caution. Handle this apparatus very carefully. Do not use a 
wrench to tighten or loosen the cover.) 

A . Parts of the mechanism : 

a. The safety valve, consisting of a ball which covers an opening 
in the valve seat. This ball is held in place by a spring. The 
safety valve prevents the cooker from bursting in case of excessive 
steam pressure. The pressure of the spring is overcome and the 
steam escapes when the pressure rises to about twenty-five pounds 
per square inch. The ball must be kept clean and free to move in 
the valve seat. 

b. The pressure gauge registers pressure up to thirty pounds 
per square inch. 

c. This cooker has been equipped with a thermometer for ob- 
serving changes in the boiling point due to increased pressure. 



128 



LABORATORY PROJECTS IN PHYSICS 



d. Note the sloping surfaces where the cover fits against the 
cooker. They have been carefully beveled to make an air- 

tight joint when the cover 
is screwed on. 

B. Use of the Cooker. 
It is used in the home 
(especially in high alti- 
tudes) for cooking all 
kinds of meats and vege- 
tables, such as baked 
beans, which require a 
considerable length of 
time by the ordinary 
methods. The cooker is 
operated at about twenty 
pounds pressure and re- 
quires only about one- 
third as long to complete 
the cooking as in the open 
vessel and in this way 
saves both time and fuel. 
Pressure cookers are used 
in canning vegetables. 

C. The Test. Remove 
the cover and examine 

FIG. 52. - Pressure cooker with pressure gauge and th mec hanism. (Handle 
thermometer attachments. 

with care . ) Fill the cooker 

one-third full of water. Place the cover on carefully and screw it 
down tight. Set the apparatus on the burner and heat till the 
thermometer passes the ordinary boiling point, 212 F. Now turn 
off the gas and with the point of a file lift the bar slightly from the 
safety-valve ball, letting steam exhaust till the pressure gauge indi- 
cator drops back to zero. (This operation will remove the air 




PHONOGRAPH A 

from the cooker which would tend to make the thermometer read- 
ing low in comparison with the pressure.) Now light the stove 
again and record in a table the temperatures (boiling points) for 
each pound increase of pressure up to twenty pounds. For con- 
venience in reading, avoid heating too rapidly. Then turn off 
the gas and allow the apparatus to cool. 

1. Plot on a sheet of graph-paper the boiling point curve for the 
various pressures. Indicate pressures on the vertical line and 
temperatures on the horizontal line. 

2. Pressure cookers are used extensively in Colorado. Explain. 

3. Why is it difficult to cook potatoes or beans in an open 
vessel at high altitudes? 

4. Is it possible to heat water above the boiling point in an open 
vessel ? Explain. 

5. Explain why the pressure cooker requires only one- third as 
long for the cooking process as an open vessel. 

6. How is a pressure cooker apparatus used for making puffed 
wheat? See Butler's Household Physics. 

7. Measure the diameter of the opening into which the lid fits. 
What upward pressure is exerted upon this lid when the gauge 
registers twenty pounds per square inch ? 

54. PHONOGRAPH A 

To study the operation, theory, and mechanism of a phonograph. 

MATERIALS. Phonograph ; record ; tuning fork ; long and shotf needles ; 
match ; match box ; piece of cardboard ; cardboard box ; thin wooden board 
(chalk box lid) ; lens ; screw driver. 

A. Sound. Sound is produced by a shock or disturbance in 
the air or other medium which causes waves comparable to water 
waves when a stone is thrown into a pond. When the air wave 
reaches the ear and affects the auditory nerve we hear sound. 
If the disturbances are produced very rapidly and in regular sue- 



130 



LABORATORY PROJECTS IN PHYSICS 



cession, the train of waves pounding against the ear-drum pro- 
duces the effect of a musical tone. 

1. Strike a tuning fork lightly and hold it close to your ear. 
What reasons have you for believing that the tuning fork is pro- 
ducing a train of waves? 

2. How do the air waves differ when the fork is struck harder? 




FIG. 5^. Phonograph with horn inclosed 

3. What is meant by the statement that one fork has a " high 
pitch," and another fork " low pitch " ? 

4. Strike the fork and hold it against a table top, a cardboard 
box, or a thin wooden box. Explain the effect. 

B. How the Phonograph Sounds Are Produced. Operate the 
instrument. Wind it carefully. Note the position of the starting 
lever. Place the record on the platform. In setting the needle on 
the record, place it gently. Do not scratch the record. If you 
are in doubt about any procedure inquire of the instructor. The 
sounds from a talking machine are produced by the vibrations 



PHONOGRAPH A 



caused by microscopic waves in the groove of the disk. As the 
needle point follows these waving lines, it causes a thin mica dia- 
phragm to vibrate by means of a lever to which the needle is 
attached. The vibration of the diaphragm produces the sound 
similar to the action of a telephone receiver diaphragm. This 
diaphragm is firmly held in a metal frame called the sound-box 
or reproducer. The lever which holds the needle is pivoted to 
the side of the sound-box and has its 
long arm fastened to the mica dia- 
phragm of the sound-box. Any move- 
ment of the needle causes a corres- 
ponding movement of the diaphragm. 
In one type of record the needle moves 
" up and down," in another the needle chamber' 
follows a " side to side " movement. 
In the Victrola and the Columbia 
Graphophone the indentations run 
" side to side," in the Pathe and the 
Edison they run " up and down." 
Examine the record with a magnifying 
glass. 

5. What is the position of the dia- 
phragm when the indentations run 
"side to side"? 

6. Explain why the needle arm of the lever is shorter than the 
diaphragm arm. 

7. If the indentations run " up and down," how must the dia- 
phragm be set, vertical or horizontal? 

8. When a short needle is used it shortens the needle arm. 
What effect has this upon the movement of the diaphragm arm 
and consequently upon the tone? 

C. The Needle. Needle points are commonly made of steel, 
wood, tungsten, or diamond. The two conditions which limit any 



Soft Pub be. 
Kings 




Neecf/e Point 



FIG. 54. Sound box for "side to 
side" movement of needle. 



LABORATORY PROJECTS IN PHYSICS 



make of needle are the wearing away of the needle and the wearing 
away of the record. Either effect mars the music. Too dull a 
point will injure the sides of the grooves and too sharp a point will 
wear a track of its own. 

Push the sound-box aside. Sharpen a match stick and hold it 
in the groove with your fingers. Cut two slots near the edge of a 
piece of cardboard five inches square and push the match stick 
in one slot and out the other to hold it firmly. Now place the 
point of the stick into the groove. 



To JRe sounding 
Chamber 




Wexib/e Core/ 
^D/am on d Po/n t 
FIG. 55. Sound box for "up and down" movement Edison phonograph. 

9. Explain how a thin board fastened to the needle makes the 
sound louder. 

10. Drive one of the metal needles through a thin wooden 
board (chalk box cover). Explain why a metal needle produces a 
louder tone than a wooden needle. 

11. What are some defects of wooden needles? 

12. Why should some needles not be used more than once? 

13. Play a record with a short, stubby needle, then try a long 
slender needle. Why is the former called full-tone and the latter 
half-tone ? 

14. Why are tungsten or diamond point needles desirable? 



PROJECTION LANTERN A 



133 



55. PROJECTION LANTERN A 
Nitrogen Lamp Type. 

To operate projection lanterns and study their optical and 
electrical principles. 

MATERIALS. Transparent projector (nitrogen lamp type); screen; 
;vnmeter; opaque projector (nitrogen lamp type). 



!/0 vo/t e/ectr/c currenf out/et. 




Socfcef oard 
FIG. 56. Wiring for a nitrogen lamp projection lantern. 

A. The Transparent Slide Projector Stereopticon. Connect 
the nitrogen lamp projector to a lamp socket on the no- volt line. 
Note that the essential parts are objective lens, object (slide), 
condensing lens, and source of illumination. Place a slide in posi- 
tion and adjust the objective lens to secure the sharpest image 
on the screen. Adjust the position of the nitrogen lamp to secure 
an even distribution of light on the screen and maximum illu- 
mination. 

1. If the screen is moved nearer the apparatus, how must the 
objective lens be moved to produce a sharp focus? 

2. In focusing a camera, if the object is moved closer, how 
should the camera lens be moved? 



134 LABORATORY PROJECTS IN PHYSICS 

3. How does the human eye secure a sharp focus on the retina 
for both close and distant objects? Refer to texts. 

4. Note the two condensing lenses situated between the nitrogen 
lamp and the slide. They may be considered two halves of a thick 
double convex lens. Their purpose is to concentrate the diverging 
rays from the lamp upon the slide (object). To cast a successful 
image upon the screen the object (slide) must be brilliantly illu- 
minated. How would removing the condensing lenses affect the 
image ? 

5. What effect would be produced upon the image if the nitrogen 
lamp were not placed at the center ? 

6. Diagram the apparatus, showing screen, objective lens, slide 
condensing lenses, lamp. See Millikan, Gale and Pyle, or Butler. 

7. Attach an ammeter and find how many amperes the lamp 
takes. (Caution. Get directions from the instructor. Do not connect 
the ammeter until your plan is approved by an instructor.) 

8. What is the cost of this current per hour at 10 cents per 
kilowatt hour ? Volts times amperes equal watts. 

B. The Opaque Projector. Nitrogen lamps of high power are 
sometimes used to illuminate an opaque picture, for projecting 
its image on the screen. Small types of this apparatus are known 
as post-card projectors. Larger images are obtained with a 
brilliant carbon arc light and a very large objective lens. With 
this device pictures may be produced in colors. 

9. Diagram one type of opaque projector and indicate parts 
condensing lens, objective lens, and object. See Black and 
Davis or Hoadley. 

10. Explain why a larger lens is necessary with the opaque 
projector than with the transparent projector. What effect has 
a larger lens upon the image? 

1 1 . What effect is produced upon the image by moving the source 
of illumination farther away from the object? 



THE PULLEY 

56. THE PULLEY 

To study the operation of a pair of triple tackle blocks in lifting 
a one-hundred pound weight. 

MATERIALS. Pair of triple tackle blocks; large spring balance, two 
fifty-pound iron weights; three-eighths inch rope (sash cord). 






FIG. 57. Pulleys with weights supported by four strands and by six strands, 
simpler pulleys refer to textbooks. 

Operating a Set of Pulleys. NOTE. In the use of a system of 
pulleys the ratio of weights required to establish a condition of 
balance depends upon the number of strands of rope supporting 
the movable block. In the practical application of this mechanisn} 



136 LABORATORY PROJECTS IN PHYSICS 

for lifting heavy weights the ideal conditions never hold. The 
efficiency is very much reduced by friction in the pulley bearings 
and in the rope. 

Suspend the two weights from the movable block of the 
system of pulleys. Attach the spring balance to the power side 
and pull downward till enough force is applied to cause the 100- 
pound weight to continue to move upward. 

1. State the general pulley law. Refer to text. 

2. Calculate what the pull should be in the ideal case for a 
condition of balance. 

3. How does the actual pull compare with the calculated ideal 
pull required for a condition of balance? 

4. What is the percentage efficiency of this machine? (Effi- 
ciency equals the calculated ideal pull required to support the 
weight divided by the actual pull required to lift the weight ; or, 
efficiency equals the work out divided by work in.) 

5. Allowing for inaccuracy on account of elasticity in the rope, 
how far should the power rope move when the weight lifted moves 
through one foot? 

6. Determine the efficiency of the system for lifting one fifty- 
pound weight. 

7. Disregarding friction, is more work done on one side of such 
a machine than on the other? State the work law involved. 

8. Do we ever get more work out of a machine than we put 
in? Do we ever get as much in useful work? 

9. Which one of the following simple mechanical appliances 
involves the least friction lever, pulleys, or jackscrew ? Which 
has the greatest friction? 

10. Suggest two means of reducing friction in bearings. It is 
usually not considered advisable to use a block of more than three 
pulleys because of friction in the bearings. 

11. Mention at least two practical situations in which pulleys 
might be used for lifting. 



THE PUMP KITCHEN LIFT PUMP 



137 



57. THE PUMP KITCHEN LIFT PUMP 
To study the action of a pump. 

MATERIALS. Kitchen suction pump; wrench; two large jars or pails. 
Parts cylinder; piston (plunger) ; piston- valve ; foot- valve. 




FIG. 58. The lift pump and the force pump. 

A. The Parts and their Operation. With a wrench take the 
lift-pump apart and examine the cylinder, piston, and valves. Put 
the parts together and operate it. A lift pump (suction type) is 
of practical value for lifts of not more than 20 to 25 feet. It 
is difficult to obtain a sufficient vacuum in the cylinder for higher 
lifts. For higher lifts it is necessary to place the cylinder near 
the surface of the water or under the water, with a rod reaching 
down through the lift-pipe to the cylinder at the bottom of the 
well. In such cases it is preferable to have the cylinder under 
water. 



138 LABORATORY PROJECTS IN PHYSICS 

1. Make two diagrams, one showing the valves as the piston 
moves upward, the other as it moves downward. Explain the 
operation. 

2. How does the action of a lift pump depend upon the pressure 
of the atmosphere? 

3. Theoretically how high should a lift pump raise water by 
suction? How high should it raise mercury? How high should 
it raise alcohol? (Specific gravity, eight- tenths.) 

4. Explain the practice of pouring water above the piston to 
aid in starting the action of a suction pump. 

5. The water level in a well is sixty feet below the mouth of 
the pump. When the lift pipe is full of water what downward 
pressure will this water column exert on the face of a pump piston 
located under the water, if the area of the face of the piston is four 
square inches? 

6. If the pump handle in question five has a leverage in the 
ratio of six to one, what downward force at the handle will be 
required to raise the piston (disregarding friction)? Refer to 
text levers. 

B. Characteristics of a Deep Well Pump with Cylinder at the 
Bottom. The pump-body should be of strong material and of 
good workmanship to withstand high pressure. A good pump for 
hand use should have a stroke of from six to ten inches with rocking 
fulcrum. The piston rod should move in perfect alignment. 
The handle leverage should be approximately six to one and the 
lift pipe not less than one and one-half to two inches diameter. 
A small pipe offers too much friction. It should be so constructed 
that the valves and piston are easy of access for repair. When 
the pump is exposed to freezing temperatures, it should have a 
small drain valve below the floor to allow the water to slowly 
drain out from above the frost line and prevent freezing. The 
lifting force required in such a pump will depend chiefly upon two 
conditions the height to be lifted and the size of the cylinder. 



SAUCEPAN CONDUCTION 139 

The size of the cylinder and the length of stroke determine the 
amount of water lifted with each stroke. The cylinder of a good 
pump should be either of brass -or brass-lined, because iron, in time, 
becomes rusted. This results in leakage around the piston. 

7. Diagram a deep well pump. See Mechanics of the Household 
Keene. 

C, Repairs. The parts of an ordinary pump which need most 
attention are the leather valve parts and the leather lining of the 
piston. In the deep well, high pressure pumps these parts are 
metal. Leather parts of a pump may be renewed by any one 
having ordinary mechanical skill. The leather for these parts 
should be fairly thick and pliable. 



58. SAUCEPAN CONDUCTION 
Effect of differences in material. 

To determine the efficiencies of three saucepans, enamel ware, 
aluminum, and copper, for heating water. 

MATERIALS. Gas meter; gas burner; four-quart saucepans of enamel, 
aluminum, and copper; Fahrenheit thermometer; copper quart measure; 
screw clamp ; clock. 

NOTE. For diagram of apparatus refer to Experiment 41, Gas Stove Burner. 

To what extent do differences in material affect the amount of 
heat conducted through the walls of a four-quart vessel? (The 
gas flow is kept constant at the rate of one cubic foot in four 
minutes.) 

A. Attaching the Meter and the Burner. Connect a piece of 
rubber tubing from the gas cock to the side of the meter marked 
" inlet." Attach the burner to the other side of the meter. Place 
a screw clamp on the tube between the meter and the burner. 
(Caution. Allow a quarter of a cubic foot of gas to flow through the 
meter before lighting.} Adjust the clamp by opening and closing so 



140 LABORATORY PROJECTS IN PHYSICS 

that exactly one cubic foot of gas flows through the meter in four 
minutes as indicated by the second-hand of the clock. 

Measure carefully two quarts of- water and heat it in a four- 
quart saucepan to 75 F. Stir to insure a uniform temperature. 
When the temperature of the water reaches 75 F., record the read- 
ing of the gas meter. Place a cover on the vessel and allow the 
heating to continue till one cubic foot of gas has been consumed. 
Readjust the screw clamp each minute to keep the meter hand in 
step with the second hand of the cl6ck. Remove and stir, noting 
the final temperature. 

1. How many B.T.U. passed through the walls of the vessel 
into the water? (Pounds times degrees rise.) (One quart of 
water weighs two and eight-hundredths pounds.) 

2. What per cent of the total heat of the flame entered the 
water? (One cubic foot of gas gives out 600 B.T.U. heat 
of combustion.) This result will represent the thermal efficiency 
of the saucepan. 

3. What principle of heat is represented in the transfer of heat 
from the flame through the metal to the water in the vessel? 

B. Aluminum Vessel. Repeat the experiment, using an alumi- 
num vessel. 

C. Copper Vessel. Repeat the experiment, using a copper vessel. 

4. Arrange data in columns as follows: starting temperature, 
final temperature, cubic feet of gas consumed, B.T.U. generated 
by the gas, B.T.U. received by water, percentage efficiency. 

59. SEWING MACHINE A 

To study the mechanical operation of a sewing machine. 
MATERIALS. Singer machine No. 20. 

Locate the following parts : balance wheel, the large needle bar 
lever, needle bar, the presser bar and presser foot, presser bar 
lifter, feed dog carrier and feed dog, looper, stitch regulator. 



SEWING MACHINE A 



141 




FIG. 59. Singer sewing machine No. 20. 



A Spool Pin 

B Thread Pull-off 

C Thread Hole in Nipper Lever 

D Nipper Lever 

K Tension 



F Thread Hole in Arm 
G Thread Hole in Needle Bar 
H Presser Foot 
I Presser Bar 
K Presser Bar Lifter 



L Stitch Regulator 
M Looper 
N Balance Wheel 
O Balance Wheel Handle 
P Guide 
Q Guide Screw 



142 LABORATORY PROJECTS IN PHYSICS 

1. Why do some mechanical devices have heavy balance 
wheels ? 

2. What causes the looper shaft to revolve at a faster rate 
than the balance wheel? 

3. How is the rotary motion of the cog wheel on the looper 
shaft changed to the linear motion of the needle bar? Explain by 
making a simple diagram. 

4. What mechanical result is obtained by making the one arm 
of the needle bar lever longer than the other? 

5. When the needle bar is approaching its highest point, what 
should be the motion of the feed dog? Explain why. 

6. When the needle bar is at its lowest point, what should be 
the position of the point of the looper? 

7. What causes the feed dog to move away from the person 
sewing ? Note that the looper and the feed dog cam are attached 
to the end of the looper shaft. 

8. What pushes it back? 

9. What varies the distance through which the feed dog carrier 
may be moved? 

10. What effect is produced upon the feed dog by pushing the 
stitch regulator up? 

11. What adjustment would you make to obtain the longest 
stitch? 

C. Threading and Oiling the Machine. 

12. Name the parts of the machine which the thread touches 
in passing from the spool to the needle. 

13. Locate and list the places on this machine which involve 
friction and on which oil might be put. 

14. What are two important advantages obtained by the 
proper oiling of a sewing machine? 



WATER MOTOR A 



60. WATER MOTOR A 

To study water motors and water power. 
MATERIALS. Water motor ; gallon measure ; quart measure. 
A. Calculated Horse Power. Operate the motor and catch 
in the gallon measure the water which it uses. 

1. With a clock and a gal- 
lon measure, find how many 
seconds are required for one 
gallon of water to pass through 
the motor. At this rate find 
how many cubic inches of water 
pass through the motor in a 
minute of time. (One gallon 
equals two hundred and thirty- 

- efte cubic inches.) 

2. Note the pressure at this 
faucet in pounds per square 
inch while the motor is in opera- 
tion. 

3. Find the foot-pounds of 
work represented per minute 
by the cubic inches of water 
used and the pressure at the 

-faucet. (Divide the number 
of cubic inches per minute by 
twelve to get feet of water 
with cross section of one square 

inch. Multiply by the pres- FI G- 60. Water motor with pressure gauge 

attached, 
sure in pounds per square 

inch to get foot pounds of work represented per minute.) 

4. Calculate the horse power represented by this amount of 
work per minute. (Foot pounds done per minute divided by 




144 LABORATORY PROJECTS IN PHYSICS 

33,000.) Waterwheels do not develop all the power represented 
by the water used. They are usually from seventy to ninety per 
cent efficient. The actual horse power delivered by a motor should 
be determined by a brake test. Efficiency equals work out 
divided by work in, or power got out divided by power put in. 

5. If this motor had an efficiency of seventy-five per cent, 
what would be its horse power? 

6. Calculate the cost of running the motor for ten hours at 
one dollar per thousand cubic feet of water. 

7. How much work in foot pounds is represented by a dollar's 
worth of water at the pressure of the faucet? 

8. What horse power is represented by a flow of six gallons of 
water per minute at sixty pounds pressure? This would operate 
a laundry washing machine. 

9. What would this water cost per hour at one dollar per 
thousand cubic feet? List two or more possible uses for a water 
motor in the home. 

B. Reference Work. Waterwheels and Water Power. 

a. Practical Physics Black and Davis. 

10. Explain how the water motor works. 

11. Name two old and two modern types of waterwheels. 

12. To which type does the faucet water motor correspond? 

13. Under what conditions are Pelton wheels most commonly 
used and under what conditions are turbines most commonly used ? 

b. General Science Barber. 

14. Name the two biggest water power plants in the United 
States. 

15. What horse power is developed at Niagara? 

1 6. About how far from these great hydro-electric plants is it 
profitable to transmit this power by electricity? 

17. To what city and how far is most of the power generated 
at Keokuk sent? 



ALTERNATING CURRENTS 



145 



GROUP III. EXPERIMENTS 
61. ALTERNATING CURRENTS 

NOTE. This experiment should be preceded by the experiments 
on the electric motor and the electric generator. 

To study alternating currents. 

MATERIALS. Pocket compass; large steel file, one in. wide by ten in. 
long, magnetized; telephone magneto; battery voltmeter; electric bell; 
dry cell. Motor-generator set used in Electric Motor B with alternating 
current armature. (Part of this apparatus must be obtained from the instruc- 
tor.) 



Pockef 
Compass 




Co/7 conta/nintp 
/O00 turns 



Dry ce// 




FIG. 61. Apparatus and wiring for the study of alternating currents. 

A. Introductory Experiments. Take the two large coils off 
the motor-generator apparatus and place them on the table. Con- 
nect two insulated wires each three feet in length to the terminals 
of one of these coils. Place the coil on the table in position so that 
it lies with opening horizontal. Set the pocket compass on the 
top of the coil. Move the coil in such position that its opening 
stands east and west. 



146 LABORATORY PROJECTS IN PHYSICS 

1. Touch the free ends of the two wires to the two terminals 
of a dry cell. Does the needle on the coil remain parallel to the 
wires of the coil? What position does it take while the dry cell 
current is flowing through the coil? 

2. What effect is produced upon a coil by a current passing 
through it? 

3. What causes the compass needle to change its position when 
a current passes through the coil ? 

4. How can you reverse the direction of current flow through 
the coil? 

. 5. What effect has this upon the polarity of the coil? 

6. When the current through the coil is reversed, how is the 
position of the north pole of the compass affected? Observe 
closely. By reversing the flow of this dry cell current, you produce 
the effect of an alternating current upon the coil. An alternating 
current flows first in one direction, then in the opposite direction. 

7. How does an alternating current differ from a direct current 
in its magnetic effect upon a coil through which it is flowing? 

B. Alternating Currents Produced Mechanically. Remove the 
dry cell and connect the two coils together by means of two three- 
foot wires. Pass a large permanent magnet (magnetized large 
steel file) quickly into the coil just attached and observe the effect 
upon the compass on the other coil. 

8. What evidence have you that this magnetism cutting 
through the turns of the coil generated a current? 

9. Quickly pull the permanent magnet out of the coil. What 
effect did this produce upon the other coil? 

10. When a magnet approaches the opening of a coil the current 
flows in one direction and when it recedes from the coil the current 
flows in the opposite direction. How can you prove this? If the 
coil of wire moves instead of the magnet, the same effect is pro- 
duced. This illustrates the fundamental operation of all mechan- 
ically generated currents in dynamos and magnetos. 



ALTERNATING CURRENTS 147 

C. The Telephone Magneto. 

ii. Explain how this device produces an alternating cur- 
rent. Connect a small lamp to it and see if it gives current 




FIG. 62. Generator with alternating current armature. 

enough to light the lamp. Magnetos are used for ignition pur- 
poses on gas engines, and for ringing some types of telephone 
bells. 

12. Connect the telephone magneto to a battery voltmeter 
and operate it. What evidence have you that the current it 
produces flows in pulses or alternates? 



148 LABORATORY PROJECTS IN PHYSICS 

D. The Alternating Current Generator. Put the coils back 
on the motor generator apparatus and set the alternating current 
armature in position. Send the current of two dry cells through 
the field coils to produce the magnetism. Run the armature by 
means of a belt from a motor or some other source of power. 
Ask the instructor for a lamp of suitable voltage. Do not attach 
a lamp without the instructor's advice, as it may be ruined. 

E. Reference Work Practical Physics, Black and Davis. 

13. Why is alternating current used in city distribution? 

14. For what purpose are transformers used? 

15. What are some voltages used in long distance transmission? 

62. CAMERA B 

To study some optical principles and the operation of a 

camera. 

MATERIALS. 4X5 focusing camera with plate-holder and rapid recti- 
linear lens ; simple lens ; foot rule ; screen. (Part of this apparatus must be 
obtained from the instructor.) 

A. The Camera. A camera is a delicate piece of mechanism. 

Handle it with extreme care. Do not try to manipulate any part 
of it unless you feel certain that you understand what to do. If 
you are in doubt about any manipulation, ask the instructor. Do 
not take chances with an expensive piece of apparatus. If any 
part of the mechanism does not seem to work readily, do not force 
it. Ask the instructor. Never touch the lens with your fingers 
or other object not especially intended for cleaning it. 

Open the camera by pressing the button which holds the door 
shut. The instructor will then show you how to draw the lens 
out until the indicator reaches the focusing scale. In some cameras 
a small wheel at the side of the focusing scale enables you to move 
the lens in focusing, toward the ground glass (screen) or away 
from it, depending upon the distance from the lens of the object 
to be photographed. This distance is given in meters and in feet. 



CAMERA B 149 

B. Lenses. 

1. Measure the focal length of one of the reading glass lenses 
by focusing the sun's rays to the smallest possible spot on a sheet 
of paper. Measure the distance in inches from the center of the 
lens to the point of focus. If the sun is not shining, get the focus 
of some distant object on the screen and measure the distance 
between the screen and the center of the lens. 

2. Find the focal length of the camera lens. Set it toward the 
sun and focus on the center of the ground glass or focus on some 
distant object. Measure approximately the distance from the 
center of the lens combination to the ground glass. 

3. What is the diameter of the lens? 

4. What is the /-value of this lens? (The /-value is found by 
dividing the focal length by the diameter.) The highly corrected, 
expensive, anastigmat lenses are of large aperture, having a low 
/-value. These lenses make very bright images and take snap- 
shots as rapid as one-thousandth of a second. 

5. What is an achromatic lens? See Millikan, Gale and Pyle, 
or Carhart and Chute. 

6. Diagram a two-piece achromatic lens. 

7. What two kinds of glass are used in making an achromatic 
lens? Refer to texts. 

8. The larger cameras and projection lanterns usually have 
double combination lenses known as " rapid rectilinear " lenses. 
Diagram and describe a rapid rectilinear lens. See Black and 
Davis or How to Make Good Pictures. 

9. What is an anastigmat lens? Some of these lenses cost as 
much as fifty to a hundred dollars. They sometimes are com- 
posed of six or eight different lens parts. What are some of the 
advantages of an anastigmat lens? See How to Make Good 
Pictures. 

10. Name three defects or aberrations of simple lenses made of 
a single piece of glass. See The Wonder Book of Light Aberra- 
tions of Lenses. 



150 LABORATORY PROJECTS IN PHYSICS 

11. Examine the shutter dial. How many different adjust- 
ments for timing of the exposure are available on this camera? 
Name them. 

12. Examine the stop scale. Should the stop be set high or 
low for a very rapid exposure ? Why ? 

13. If the stop is more nearly shut the picture is sharper than 
when it is wide open. What disadvantage is involved in closing 
the stop ? When should the stop be opened ? When closed ? 

C. Focusing. Focus the camera on some near-by object six 
or eight feet away. In focusing move the lens forward and back 
until the point of sharpest image is produced upon the ground 
glass. Focus sharp on an object at six or eight feet distance. 
Without changing the distance between lens and ground glass, 
observe the image of a building or other object at a distance of 
several hundred feet. 

14. To make the focus sharp at the greater distance should the 
lens be moved toward the ground glass or away from it ? 

15. Make a simple diagram to illustrate these differences in 
focus. See How to Make Good Pictures. 

63. CAMERA C 
Exposing, Developing, and Making a Print. 

To make a print from a negative. 

MATERIALS. Negative; printing frame; Aristo Gold Paper (Eastman 
Kodak Co.) ; hypo ; sodium carbonate ; table salt ; teaspoon ; glass graduate 
(in ounces) ; one glass tray ; two enamel trays. (Part of this apparatus must 
be obtained from the instructor.) 

NOTE. Exposing, developing, and fixing the negative require too much 
technique and time to be done during the regular laboratory hour. This 
procedure will be described in brief below. If groups of six students can arrange 
to meet with the instructor at a convenient time outside of the regular class 
period the making of a negative may be demonstrated. As a reference book 
use How to Make Good Pictures, Eastman Kodak Co. 



CAMERA C I$I 

A. Exposing, Developing, Fixing, and Washing the Negative. 
(NOTE. This work is to be omitted except by special arrangement 
with the instructor at some special time.) 

Exposing! For general outdoor work it is a good practice to keep 
the stop at some fixed point, as No. 8 stop, and become familiar 
with the shutter time required for changes in light intensities such 
as exposures in shade, in medium light, or in sunlight. For indoor 
work and for pictures taken in the evening, it is often necessary to 
open the stop wider and to increase considerably the time of ex- 
posure. Indoor exposures require about one hundred times as long 
as outdoor exposures if the stop opening is the same in both cases. 

Developing and Fixing. The developing solution is made by 
taking eight ounces of water in a graduate with the contents of 
one developing tube. Stir with a clean glass rod until completely 
dissolved. Do not pour developer into the developing tray until 
the plate is in it. If developer is kept from one day to the next, 
keep it corked up in a bottle. (Caution. Never put developer into 
a fixing tray or fixer into a developing tray. After putting your 
fingers in the fixing bath never put them into the developing solution 
without first washing them and drying with a towel. If a drop of the 
fixing solution gets into the developer it will be injured or ruined. 
Proceed slowly; be sure you know what to do; think before you act.) 
The time for developing is ten to fifteen minutes. The develop- 
ing solution (reducing agent) changes the white silver salt to 
black metallic silver. The white silver salt is changed to black 
silver metal only if it has been exposed to light. Those parts of 
the plate which have had no light are not blackened by the 
developer. The dark parts of a negative or print are silver metal. 
It is advisable to move the tray slightly while developing. The 
developing process must be observed with a ruby lamp. When 
the negative (picture) is completely developed, it is dipped in 
water and transferred to the fixing bath. The fixing solution is a 
solution of hypo (sodium thiosulfate) dissolved in water one 



152 LABORATORY PROJECTS IN PHYSICS 

ounce of salt to four ounces of water. Before beginning the de- 
veloping, fill the fixing tray one-quarter full of fixing solution and set 
it aside for use when the plate is developed. The purpose of the 
fixing solution is to dissolve out of the emulsion all silver bromide 
which has not been changed to silver metal by the action of light 
and the developer. The fixing requires about fifteen minutes. The 
fixing is complete when all white has disappeared from the negative. 

Washing. When fixing is completed, remove and place the 
plate in running water for one-half hour. Plates will discolor if 
not completely fixed or properly washed. After washing, stand the 
plate up to dry. When the emulsion is dry, prints may be made. 

B. Making a Print from a Negative. Place the plate in the 
printing frame. Place a piece of Aristo Gold printing out paper 
(Eastman Kodak Co.) in the printing frame so that the emulsion 
sides of the paper and of the plate meet. Stand the printing 
frame facing the sun. The time of printing will depend upon the 
density of the negative and upon the brightness of the light. The 
progress of the printing may be observed by carefully releasing 
one side of the printing frame and raising the paper. This should 
be done in the shade. The print should be made consideTably 
darker than is desired in the finished picture since it bleaches out 
in the fixing bath. The chemical principle is essentially the same 
as in the making of a negative. 

NOTE. The more rapid developing papers require a dark room 
for developing, a developing solution and some practice in 
manipulation. 

C. Toning the Print. Prepare the salt bath, the soda bath, 
and the fixing bath described below before beginning the work. 
(Caution. Always use the glass tray for the fixing bath in order to 
keep hypo away from the developing and toning trays.} " Printing 
out " papers, like Aristo Gold, usually require a toning bath, 
while " developing out " papers, like Velox, require a developing 



CAMERA C 153 

bath similar to that of a negative. Aristo Gold requires a very 
simple toning procedure. (Always wash trays before and after 
using.) Place prints face downward in a solution of one-quarter 
ounce of table salt (level teaspoon) in sixteen ounces of water. 
Keep prints in motion until they turn to a purple tint (about ten 
minutes). Rinse in water containing enough sodium carbonate (sal 
soda) to make it feel smooth (level teaspoonful). Prints should 
remain in the soda bath about three minutes, then be removed to 
the fixing bath. This process gives a purple tone. If a carbon 
sepia tone is desired omit salt and soda baths. Wash prints directly 
in six changes of water and place them in the fixing bath. 

D. The Fixing Bath. (Caution. Prepare the fixing solution 
always in the same tray. Use the glass tray for fixing bath. Never 
make up a fixing bath in any other tray.} Dissolve one ounce (four 
teaspoonfuls) of hypo (sodium thiosulfate) in eight ounces of 
water. Move prints about in fixing bath fifteen or twenty min- 
utes, wash in ten changes of water. Dry between blotters. 

E. Reference Work. How to Make Good Pictures. 

1. What is meant by the term " orthochromatic plate"? 

2. Why does a small stop opening on a common lens give a 
sharper focus than a large stop ? 

3. What type of lenses give sharpest pictures for large stops? 

4. Under what conditions should a small stop be used? 

5. State the speed and the uses of the fastest shutters. 

6. Which gives greater depth of focus (focus for objects that 
are near and far), a large stop or a small stop? 

7. Why should the sun not shine toward the face of the lens? 

8. Give normal temperatures for developing and fixing baths. 

9. If a plate were exposed to the light after it is developed 
and before it is fixed, explain why it would be ruined. 

10. Why does a white dress appear black on a negative? 

11. How does black on a negative produce white on the print? 

12. State four directions preliminary to making a snapshot. 



154 LABORATORY PROJECTS IN PHYSICS 

%. THE ELECTRIC DISK STOVE 
Heating Water Cost and Efficiency. 

To determine the cost of heating a quart of water from 75 F. 
to the boiling point, 212, when heat is obtained from an 
electric disk stove. 

MATERIALS. Disk stove; Fahrenheit thermometer; copper quart 
measure ; 4-quart saucepan ; socket ; wires ; gas-burner ; clock. 



Electric Current Out/et 



A ttachm en t 




ffectrk Stove orffotP/ate 

Socket fioard 
FIG. 63. Wiring for the electric stove. 

Assume that the amperage and voltage ratings on the label of 
the heating device are correct unless otherwise stated by the 
instructor. Complete wiring connections from the socket to the 
line terminals before attaching the stove. Current should be 
turned on and off from a heating element which uses three or 
more amperes by an attachment plug, not by screwing into a 
socket or by turning an ordinary button. The reason for this 
precaution is that a large current (amperage) produces a very 
hot spark and will melt the metal of the socket if it is not discon- 
nected quickly and completely. 

A. Heating by Electric Disk Stove. Measure carefully a 
quart of water into the saucepan. Heat this water to the starting 
temperature, 75 F., on a gas-burner. Stir to get a uniform 
temperature reading. When the temperature reaches 75 attach 



THE ELECTRIC DISK STOVE 



155 



the plug, sending current into the disk stove. (Caution. Do not 
heat a disk stove for more than a few minutes without some vessel on 
it, as it may become overheated and ruined.) Note the starting time 
on the clock and place the vessel of water with cover on the stove. 
Allow the heating to continue till the water reaches the boiling 
point as indicated by the evolution of steam bubbles (not air 
bubbles) from the bottom of the vessel. Note the stopping time 
and disconnect the heating utensil from the electric lines by pulling 
the attachment plug from its socket. 

1. How many amperes of current does this device use? 

2. What is the voltage of the line? Read the line voltmeter. 

3. How many kilowatt-hours of electric energy were used? 
(Volts times amperes divided by one thousand and that result 
multiplied by the number of hours in operation.) 

4. What was the cost of this heating at ten cents per kilowatt- 
hour? 

5. How many B.T.U. did the water receive? (Pounds of 
water times degrees rise.) (One pound equals four hundred and 
fifty-four c.c.) 

6. How much heat was generated by the electric energy which 
you used? (One kilowatt-hour gives out thirty-four hundred 
B.T.U.) 

7. What per cent of the total heat of the electric energy used 
entered the water? This result represents the heating efficiency 
of the operation. 

B. Electric Heating Elements. 

X^A>A-t *- f\ 

8. , Diagram the heating wires in an electric disk stove, a flat- 
iron, or an electric toaster. See Keene, Butler, or Hoadley. 

9. What result would you expect if this device were attached to 
a current of half the voltage rated for its use ? 

10. Describe how the heating wires are insulated from the 
metal of an electric iron or toaster. See Keene. 



156 



LABORATORY PROJECTS IN PHYSICS 



65. THE ELECTRIC GENERATOR (DYNAMO) 
To study the construction and operation of an electric generator. 

NOTE. It is preferable to take the experiment dealing with the 
" Electric Motor " preliminary to this experiment. Handle ap-. 
paratus carefully. 

MATERIALS. Small generator, operated by hand power (L. E. Knott 
hand power dissectible dynamo and motor) ; small lamp ; battery ammeter ; 
battery voltmeter ; electric bell ; small motor ; telephone magneto generator. 
(Part of this apparatus must be obtained from the instructor.) 




FIG. 64. Electric generator. 

A. Explanation and Operation. In construction the simple 
generator is the same as the simple motor. The simple generator 
is a device for revolving a coil of wire between the poles of a strong 



THE ELECTRIC GENERATOR (DYNAMO] 157 

electromagnet. When a magnet moves into a coil or away from 
it, a current is generated in the coil. Or if a coil revolves in the 
presence of a magnet, a current is generated in the coil. The coil 
cuts the lines of force produced by the magnet. (The wires lead- 
ing from the coil must be connected to complete a circuit.) 

Operate the small hand-power generator. Connect wires to it, 
causing it to ring a bell, light a small lamp, and run a small motor. 

1. Attach a battery voltmeter to the terminals and measure 
its voltage at your maximum speed. 

2. Attach a battery ammeter in series with a small motor, 
and measure the amperage which passes through it at your maxi- 
mum speed. 

3. How does varying the speed affect the voltage? As the 
voltage increases the amperage also increases through a given 
resistance. 

4. Make two simple diagrams of generators showing series 
winding and shunt winding. See Black and Davis. 

5. If a generator armature contains a commutator, will the 
current be direct or alternating ? 

6. What is the function of the field coils of an electric gen- 
erator ? 

7. Of what material are the brushes in this small generator 
made ? in large generators and motors ? 

8. How does a generator get its field magnetism? Refer to 
texts. At the beginning a very small amount of residual magnet- 
ism remains in the magnets from the last running to start the 
voltage in the armature, which in turn starts a small current. 

B. Telephone Magneto Generator. Operate this generator 
and attach a small lamp. This device is sometimes used on tele- 
phone instruments for the purpose of ringing up the party at the 
other end of the line. 

9. How does its field magnet differ from that of the regular 
generator? 



158 LABORATORY PROJECTS IN PHYSICS 

10. If the armature shaft contains rings in place of a commu- 
tator, what kind of current does it deliver? 

C. Demonstration Generator. The same apparatus used for the 
experiment with the motor should be used as a large generator. It 
may be operated by another motor or it may be connected by belt 
to a one and one-half horse power gas engine as a source of power. 

11. With a suitable voltmeter measure its voltage. Ask in- 
structor for the voltmeter. 

12. Wire it as a shunt generator. 

13. Attach a motor of proper size and measure the amperes 
of current which it consumes. 

14. Name five essential parts of a generator. (Same as in a 
motor.) 

15. Diagram a compound wound generator. 

66. THE ELECTRIC IMMERSION HEATER 
Heating Water Cost and Efficiency. 

To determine the cost of heating a quart of water from 75 F. 
to the boiling point, 212, when heat is obtained from an 
electric immersion heater. 

MATERIALS. Immersion heater; Fahrenheit thermometer; copper 
quart measure ; 2-quart vessel ; socket ; wires ; gas-burner ; clock. (Part of 
this apparatus must be obtained from the instructor.) 

Assume that the amperage and voltage ratings on the label of 
the heating utensil are correct, unless otherwise stated by the 
instructor. Complete wiring connections from the socket to the 
line terminals before attaching the utensil. Current should be 
turned on and off from a heating element which uses three or more 
amperes by an attachment plug, not by screwing into a socket, or 
by turning a button. The reason for this precaution is that a large 
current (amperage) produces a very hot spark and will melt the 
metal of the socket if it is not disconnected quickly and completely. 



THE ELECTRIC IMMERSION HEATER 



159 



A. Heating by Immersion Heater. Carefully measure one 
quart of water into the vessel. The water in the vessel should 
completely cover the heating element of the immersion heater. 
Heat this water to the starting temperature, 75 F., on a gas- 
burner. Stir to get a uniform temperature reading. When the 
temperature reaches 75 attach the plug, sending current into the 
immersion heater. (Caution. Do not heat an immersion heater out- 

//ff vo/t e/ectr/'c current out/et 

f 









Socket oard ff eater' 

FIG. 65. Wiring for the electric immersion heater. 

side of the water, as it may become overheated and ruined.) Note 
the starting time on the clock and allow the heating to continue 
till the water reaches the boiling point, as indicated by the evolu- 
tion of steam bubbles (not air bubbles) from the bottom of the 
vessel. Note the stopping time, and disconnect the heating utensil 
from the electric lines by pulling the attachment plug from its socket. 

1. How many amperes of current does this device use? 

2. What is the voltage of the line? See laboratory line volt- 
meter. 

3. How many kilowatt-hours of electric energy were used? 
(Volts times amperes, divided by one thousand, and that result 
multiplied by the number of hours in operation.) 



160 LABORATORY PROJECTS IN PHYSICS 

4. What was the cost of this heating at ten cents per kilowatt- 
hour? 

5. How many B.T.U. did the water receive? (Pounds of 
water times degrees rise.) (One pound equals four hundred and 
fifty-four c.c.) 

6. How much heat was generated by the electric energy which 
you used? (One kilowatt-hour gives out thirty-four hundred 
B.T.U.) 

7. What per cent of the total heat of the electric energy used 
entered the water? This result represents the heating efficiency 
of the operation. 

B. The Immersion Heater. 

8. If you have performed the same operation with the disk 
stove, compare the two costs. Why is an immersion heater more 
efficient than a disk stove ? 

9. By what principle of heat transfer does heat pass from the 
heating element into the pan? 

10. How might screwing this device from a socket instead of 
pulling apart the plug cause a fuse to blow out ? See Butler: 

67. ELECTRIC MOTOR B 

Direct Current. 

To study the construction and operation of electric motors. This 
experiment should be preceded by Electric Motor A. 

MATERIALS. Four dry cells ; battery ammeter ; wires ; commercial 
types of motors ; motor generator set ; compass ; screw driver ; wrench. 

A. Construction of the Motor. With a screw driver and 
wrench, disassemble the apparatus, removing the armature shaft, 
brushes, and field coils. 

1. How many commutator segments has this motor? 

2. How are the brushes held against the commutator when 
the motor is operating? 



ELECTRIC MOTOR B 



161 



3. Of what material are the brushes made? 

Reassemble the motor for operating. Wire it in series. Con- 
nect four dry cells in series with a battery ammeter and measure 
the amount of current the motor lets through with the voltage of 
four dry cells. 




Commutator 
Armature 

FIG. 66. An electric motor or generator with parts disassembled. 

4. What is the voltage of four dry cells ? 

5. What amperage passes through the motor at this voltage? 

6. What is the resistance of the motor in series? Apply 
Ohm's law (volts divided by ohms equal amperes). 

B. Operation. 

7. Do not attach this motor to the no- volt line without having 
the wiring approved by an instructor. Calculate the amperage 
which would pass through this motor if it were attached to the no- 
volt line without resistance. This amount of current would pass 
through it if the armature were not permitted to revolve. Note 
that a motor takes more current through it if the armature is not 
allowed to revolve, or if it is made to do work. Apply Ohm's 



1 62 LABORATORY PROJECTS IN PHYSICS 

law. A motor should not get hot in operation. If a rheostat is 
needed, the instructor will give directions for attaching it. 

8. What is meant by counter electromotive force, or counter 
voltage produced by a motor armature when it begins to revolve ? 
See Elements of Electricity Timbie. If the motor does not run 
when current passes through, test the field poles with a compass. 
How should the poles test? 

9. If the poles are of like sign, how can they be made unlike? 

10. How many amperes are required to run this motor? At- 
tach an ammeter. 

11. Calculate the horse power that this motor should have if 
all electric energy used were transformed into mechanical energy. 
(Volts times amperes equal watts. Seven hundred and forty-six 
watts equal one horse power.) 

12. What is meant by percentage efficiency of an electric motor ? 
See Black and Davis. 

13. Diagram a shunt wound motor. See Hoadley, or Carhart 
and Chute under Dynamo. 

14. Diagram a compound wound motor. 

15. Measure the current in amperes required to operate a 
motor for some specific purpose, such as a fan motor, a vacuum 
cleaner motor, etc., and calculate its cost per hour. Ask the 
instructor for a suitable motor. 

C. Characteristics of Motor Winding Shunt, Series, and Com- 
pound. 

a. Shunt. This is the most common type of motor. It usually 
has a starting resistance through which the armature current must 
flow. The chief advantage of the shunt motor is that it has fairly 
constant speed with load or no load. It does not race except 
when the current through the field is excessively reduced, thus 
reducing counter voltage. 

b. Series. Speed depends entirely upon the load. It should 
never run disconnected from its load, as it may increase in speed 



GASOLINE ENGINE B 163 

till the armature bursts. Its common uses are in street railway 
cars, in fans, automobile starters, etc., where it is always attached. 
It furnishes a strong starting torque. 

c. Compound. Motors are wound compound where load is sub- 
ject to variations, and nearly constant speed is desired, as in op- 
erating shop machinery which are periodically thrown on and off. 

68. GASOLINE ENGINE B 
To operate a gas engine and explain its action. 

MATERIALS, i \ horse power gasoline engine on truck. See illustration 
of Gasoline Engine A, Experiment 42. 

A. Starting the Engine. Fill the cylinder hopper with water 
and oil the cylinder and bearings. Use illuminating gas or gasoline. 
Before attempting to start the engine throw on the spark-coil 
lever, close the air-damper (to increase the suction if gasoline is 
used), and turn the fly wheels over compression. Open the air 
damper when the engine begins to explode. If the engine is prop- 
erly timed, explosion should take place at or near maximum com- 
pression. If you are in doubt about the procedure have an in- 
structor start the engine. (Caution. Keep a safe distance from 
moving wheels and shafts.) The engine will start more readily 
if the mixing valve is opened about two turns to let in a richer 
mixture at the start. When the engine begins to run the mixing 
valve should be screwed farther shut, otherwise the mixture may 
be too rich and cause smoking at the exhaust. If the mixture 
is too lean the engine will misfire, run slow, or " gasp for breath." 

B. The Mechanism and Operation. 

1 . Can a four-stroke engine explode every revolution ? Explain. 

2. In the four-stroke engine, what is the ratio of the cog teeth 
on the two wheels which operate the cam? 

3. What is the function of the cam? 

4. Name two parts that are operated by the cam rod. 



1 64 LABORATORY PROJECTS IN PHYSICS 

5. Examine the governor. What runs it? What does it do 
to the cam rod when the speed becomes too great? Pull the 
balls apart and note how this stops the explosion when the engine 
is running. Set the speed lever in high, medium, and low. 

6. What pushes the cam rod toward the crank shaft ? What 
pushes it back again? 

7. When the engine is running, note that the cam rod operates 
a valve by means of a lever at the end of the cylinder. Is this 
the intake valve or the exhaust valve? Why? 

8. What is the purpose of the other valve? What causes it 
to open? What causes it to close? 

9. What is the purpose of the water jacket around the cylin- 
der? The water should be withdrawn from it in cold weather 
when the engine is idle. Why? 

10. When the engine speeds up to maximum, what stops the 
sparking mechanism? 

11. When the engine speeds up to maximum, what keeps the 
exhaust valve open? 

12. When the exhaust valve is kept open, does the piston 
draw in mixture through the intake valve? Explain. 

13. Why do gas engines need such heavy flywheels? 

14. List some uses in the home or on the farm for gasoline 
engines. 

(NOTE. After stopping the engine, throw out the switch at the 
spark coil in order to avoid wasting the battery current.) 



69. HORSE POWER A. ELECTRIC MOTOR 

' .. }<~j^> 

To determine the horse power of an electric motor. 

MATERIALS. Small no- volt motor attached to a ring stand; two spring 
balances; belt brake; speed indicator. (Part of this apparatus must be 
obtained from the instructor.) 

A. Horse Power. The horse power output of an electric 
motor, an engine, a water wheel, etc., refers to how much work 



HORSE POWER A. ELECTRIC MOTOR 



the source of power is able to do per second or per minute. The 
unit of work is the foot pound or the lifting of one pound vertically 
through one foot distance. In general, work done equals pounds 
lifted times the vertical distance lifted in feet. If a motor or an 



//0 vo/t F/ectr~/c Currenf Out/ef 

/ 

D 




<= 





Socket J3oard Mo for- w/th e/t Brake 

FIG. 67. Wiring and apparatus for determining the brake horse power of an electric 

motor. 

engine is able to lift 33,000 pounds through a vertical distance 
of one foot in one minute, it is able to do work at the rate of one 
horse power. A one horse power motor or engine can do 33,000 foot 
pounds of work per minute. It can lift one pound 33,000 feet in 
one minute, or 33,000 pounds through one foot, etc. To determine 
the horse power of an engine or motor, find how many foot pounds 
of work it can do in one minute, and divide this result by 33,000. 

1. How much work is done by lifting one hundred pounds 
vertically through eight hundred feet? 

2. What horse power is required to lift three thousand pounds 
one thousand feet in five minutes ? Find how much work is done 
in one minute and divide by 33,000. 



l66 LABORATORY PROJECTS IN PHYSICS 

B. Horse Power Measured with a Belt Brake. The belt brake 
attachment makes it possible to determine how many pounds the 
motor can pull in operation. The distance in feet through which 
this pull is exerted may be found by determining the number of 
revolutions per minute made by a point on the circumference of 
the pulley at which the brake is applied. Find the number of 
revolutions per minute, and multiply this by the circumference of 
the belt groove in feet. To determine the number of revolutions 
per minute, hold the speed indicator against the end of the motor 
shaft firmly enough to prevent slipping. Count the number of 
revolutions made in fifteen seconds and calculate the speed per 
minute. 

3. How many revolutions are made by the speed counter 
shaft while the dial makes one revolution (gear ratio) ? 

4. Determine the maximum speed of the motor with no load. 
Apply a slight tension by raising the belt support on the ring stand 
rod. The pull exerted on the motor is the difference between the 
readings on the two balances. If the balances read ounces, reduce 
to pounds. Note that if the tension is made great enough, the speed 
of the motor is very much reduced. (Caution. Do not allow the 
motor to run longer than fifteen seconds at one time with tension on 
the pulley as the friction on the pulley produces heat, and the motor 
may be injured by overheating.) 

5. Make at least five measurements of the pounds pull and the 
speed per minute (number of revolutions in fifteen seconds X four) , 
beginning with a very slight pull and increasing with each measure- 
ment so that the last measurement is made with enough tension 
to cause the motor to run at a comparatively slow speed. Multi- 
ply the pull in each case by the corresponding speed per minute. 
One of the products should represent the maximum. If the 
last product is greatest, you have not made the tension great 
enough and more readings should be taken. In a series of five 
products, the third or fourth should be greatest. Make a table 
showing the data for these five measurements. 



HORSE POWER B 167 

6. From the pounds pull and the revolutions per minute of the 
maximum, calculate the work done per minute. (Pounds times 
circumference of pulley in feet, times speed per minute.) 

7. From the result in question 6, what is the maximum horse 
power of this motor? (Work in foot pounds done per minute, 
divided by 33,000.) 

70. HORSE POWER B 
Efficiency of an Electric Motor. 
NOTE. This experiment should be preceded by Horse Power A. 

To compare the power got out of an electric motor with 
the electric power put in efficiency. 

MATERIALS. Apparatus used in Horse Power A ; ammeter. 

A. Attaching the Motor to the Line. With the help of an in- 
structor attach an ammeter for measuring the amperes of current 
which the motor uses. Read the voltage on the laboratory line, 
voltmeter. 

1. Does a motor use more amperes when it is running free, or 
when a brake is applied and it is required to do work? 

B. Calculating the Efficiency. Refer to your data in Horse 
Power A. Find the tension on the balances representing the maxi- 
mum product of pull and speed per second. Set the balances so 
that the motor operates under this same pull. Turn on the current 
and note the amperage consumed at this tension of the balances. 
(Caution. Do not operate the motor longer than necessary to make the 
reading. Avoid overheating on account of friction of the belt.} 

2. How many watts of power does this motor consume? 
(Volts times amperes equal watts.) 

3. What horse power is represented by this current? (One 
horse power equals 746 watts.) This represents the power put in. 

4. What horse power was got out according to the determina- 
tion in Horse Power A? Refer to data. 



168 LABORATORY PROJECTS IN PHYSICS 

5. How does the power got out compare with the power put 
in ? Efficiency equals power got out divided by the power put in, 
or work out divided by work in. 

C. Problems and References. 

6. A vacuum cleaner motor requires about one and a half 
amperes and one hundred and ten volts. What is its horse power 
output if its efficiency is eighty per cent ? 

7. A motor for operating a laundry washing machine requires 
one and two-tenths amperes and one hundred and ten volts. If 
its efficiency is ninety per cent, what is its output in horse power? 

8. A trolley car motor uses fifty amperes at five hundred volts. 
If its efficiency is eighty per cent, what horse power does it apply 
to the car? 

9. One horse power equals how many watts? 

10. What is the horse power of the following, a railroad loco- 
motive, a steamboat engine, an average horse, an average man? 
See Millikan, Gale and Pyle. 

71. HUMIDITY A 
Relative Humidity Determined from the Dew Point. 

To find the relative humidity of the air in the room at a 
particular time. 

NOTE. This experiment should be preceded by the experiment, 
Dew Point. 

MATERIALS. Data of Dew Point experiment. 

A. Relative Humidity refers to the degree to which the air 
is saturated with moisture at any particular time. Fifty per 
cent humidity means that the air has fifty per cent as much mois- 
ture as it can hold at the given temperature. Just before and 
during a rain the air may be between eighty and a hundred per 
cent saturated. Such common expressions as "muggy air," "damp 
air," " depressing air," " dry air," refer to the amounts of mois- 



HUMIDITY A 



169 



ture which the air contains at particular times. We have examples 
of high humidity in summer before a thunderstorm. In winter, 
when cold air is heated by hot-air furnaces, steam or hot-water 
radiators, the humidity in living rooms sometimes falls as low as 
ten or fifteen per cent. When cold air is heated its relative 
humidity decreases because it can then hold so much more moisture. 

It is commonly considered that a relative humidity of approxi- 
mately fifty per cent or between forty and sixty per cent is most 
conducive to health and comfort. Living rooms and schoolrooms 
on cold winter days often show relative humidities of ten per cent. 
This humidity is lower than that of the driest desert regions of 
the earth. This extremely dry air is said to contribute to nasal, 
throat, and lung diseases by drying the delicate membranes so that 
disease germs find lodgment. The woodwork and furniture of 
homes dry out and cracks appear. These close up again with 
the moist air of summer. 

B. Maximum amounts of water vapor in pounds which one thou- 
sand cubic feet of air can hold at different temperatures. (This 
means the amount of water in the air when it is completely saturated, 
or one hundred per cent humid, or at the dew point.) 



TEMPERATURE 
DEGREES F. 


POUNDS OF WATER 


TEMPERATURE 
DEGREES F. 


POUNDS OF WATER 





.08 


64 


93 


5 


.10 


68 


.06 


IS 


IS 


72 


.21 


20 


.18 


76 


32 


25 


23 


80 


55 


30 


27 


84 


75 


35 


34 


88 


.98 


40 


.41 


92 


2.23 


44 


47 


96 


2-51 


48 


54 


IOO 


2.82 


52 


.62 


152 


10.60 


56 


71 


200 


28.85 


60 


.82 







170 LABORATORY PROJECTS IN PHYSICS 

C. Calculation of the Relative Humidity from the Above Table, 
Refer to the data of the experiment on " Dew Point " and note the 
dew point temperature of the air in the room according to your 
determination. Find how many pounds of water one thousand 
cubic feet of air can hold at the dew point temperature. This is 
the amount of water actually in the air at the time. Now refer 
to the table again and see how much water a thousand cubic feet 
of air can hold at the room temperature. The relative humidity 
is the amount of moisture in the air divided by the amount which 
the air can hold at that temperature. 

'i. What was the relative humidity of the air in the room by the 
dew point method? 

D. Reference Work. General Science. Barber. 

2. How can the necessary amount of water be evaporated to 
properly humidify a room that is heated by a stove ? 

3. Diagram a hot-air furnace with a humidifying device. Ex- 
plain it briefly. 

4. How much water per hour may be necessary to properly 
humidify a typical schoolroom? 

5. Would you expect a pan of water on a radiator to properly 
humidify a room? Explain. 

72. HUMIDITY B 

Relative Humidity Determined by Means of a Wet and 
Dry Bulb Hygrometer. 

To find the relative humidity of the air in the room at a 
particular time. 

MATERIALS. Wet and dry bulb hygrometer; Humidity Tables. See 
General Science, Barber, or United States Weather Bureau Bulletin No. 235, 
Psychometric Tables. 

A . The Wet and Dry Bulb Hygrometer. This type of hygrom- 
eter consists of two thermometers. The bulb of one thermom- 
eter is kept moist by means of a wick which stands in water. The 



HUMIDITY B 



water should be at the temperature of the room. Evaporation 
from the wet bulb reduces the wet bulb thermometer reading 
below that of the dry bulb. 
If the air is dry (low hu- 
midity), the evaporation will 
be more rapid and the wet 
bulb thermometer will read 
low. If the air contains a 
high percentage of moisture, 
the evaporation will be less 
and the difference in reading 
between the two will be less. 
This difference between the 
reading of the dry bulb and 
the wet bulb may be used for 
determining humidity. Fan 
the wet bulb for about a 
minute, then read its tem- 
perature. With the dry bulb 
reading and the difference 
between the two bulbs refer 
to a relative humidity table 
and find the percentage hu- 
midity. See Barber's General 
Science. 

i. What was the rela- 
tive humidity by the Wet 
and Dry Bulb hygrometer 
method ? 




FIG. 68. A wet and dry bulb hygrometer. 



2. Why should the water in the reservoir be at room tem- 
perature ? 

3. Give a reason for fanning the wet bulb. 

4. Under what kind of weather conditions will the difference 
between the readings of the two thermometers be greatest? least? 



172 



LABORATORY PROJECTS IN PHYSICS 



5. How would you expect the thermometer readings to. com- 
pare if the instrument were placed in an ordinary living room on 
a very cold winter day ? 

Instruments have been devised to read humidity directly, such 
as hair hygrometers and those containing a compound expansion 




FIG. 69. The hygrodeik, a hygrometer containing a dial for indicating the per- 
centage humidity. 

element. Many organic materials expand and contract as a result 
of changes in humidity. They are not considered as reliable as 
the wet and dry bulb hygrometers, and they require occasional 
adjustment for accurate results. 






PHONOGRAPH B 1 73 

B. Reference Work. 

a. General Science Barber. 

6. What is the average relative humidity of your locality in 
the months of June, July, and August? See map. 

7. What is the average relative humidity of your locality in 
the months of December, January, and February? 

8. Where is the region of lowest humidity in the United States? 

9. How does moisture in the air affect personal comfort in 
winter and in summer ? 

b. Weather Jameson. 

10. How is humidity related to the feeling of warmth of a room? 

1 1 . What is a hygrodeik ? Explain briefly. 

73. PHONOGRAPH B 

MATERIALS. Phonograph; screw driver. 

A. The Tone Arm, the Horn, and the Box. The tone arm is 
the pipe which leads from the sound box to the horn. The more 
recent types of phonographs and graphophones have the horns 
concealed in the box. Some of the older models had large external 
horns for amplifying and controlling the direction of the sound. 
The quality of tones produced depends to some extent upon the 
size, shape, and material of the resonating wooden box, the larger 
cabinet types giving greater richness to the more delicate musical 
tones. 

1. How many motions must the tone arm have? Explain 
them. The length of the arm must be such that it describes as 
nearly as possible a straight line across the grooves or threads of 
the record. 

2. How is the volume of tone controlled on this machine? 

3. Can you look into the box and see the horn? Of what 
material is it made? 



174 LABORATORY PROJECTS IN PHYSICS 

B. The Motor. Ask the instructor to remove the platform 
and the screws which hold the motor in place. First unscrew the 
winding crank. Handle the motor with extreme care. The large 
rotating drum contains the tightly wound steel spring similar to 
the spring of a clock. This spring furnishes the motive power for 
driving the mechanism. Set the motor upside down in a con- 
venient position to observe its operation. Turn the starting lever 
and let it run. 

4. How many revolutions are made by the shaft which holds 
the disk platform while the spring shaft makes one revolution? 
Count them. 

5. How many cog wheels produce this effect? 

6. What is the purpose of the ratchet at the side of the drum 
which operates when the spring is being wound ? 

7. Observe the governor mechanism (two revolving metal 
weights). How do these weights prevent the mechanism from 
running too fast? 

8. What is the principle which controls this type of governor? 

9. Explain the operation of the friction pads. What part of 
the mechansim is operated by the worm-gear? 

10. What are the important mechanical results which the gov- 
ernor mechanism accomplished? 

11. Diagram a reproducer. See Millikan, Gale and Pyle or 
Household Physics Butler or Black and Davis. 

C. Reference Work. 

a. General Science Hodgdon. 

12. Explain briefly how records are made. 

13. Of what is the Edison record made? 

14. What names are given to the two types of records? 

15. Why are large needles objectionable? 

A single spoken word may contain from one to two thousand 
vibrations. Each vibration is faithfully represented by a minute 
indentation in the record groove. 



PROJECTION LANTERN B 



175 



74. PROJECTION LANTERN B 

To study the operation of a carbon-arc projection lantern. 

MATERIALS. Carbon-arc projection lantern ; large rods for ten-ampere 
arc; ten-ampere rheostat; battery ammeter; lamp socket-board. 



Out/ef for //O vo/t e/trcfric current 




fiheostat 

FIG. 70. Wiring for a carbon-arc projection lantern. 

A. Large Carbon Arc. Clamp two large projection lantern 
carbons to two ring stands and use the large ten-ampere rheostat 
in series as a resistance. Connect one wire from the line terminal 
plug to one post of the rheostat. From the other post of the 
rheostat connect a wire to one of the carbon rods on the ring stand. 
Connect a wire from the .other carbon rod to the second line ter- 
minal. Before making the attachment to the line ask the instruc- 
tor to approve your wiring plan. 

1. Operate the large carbon arc. Does more current flow 
when the carbons are touching or when the arc is burning? Ex- 
plain. 

2. If a rheostat lets ten amperes flow on the no- volt line, what 
is its resistance in ohms? Apply Ohm's Law: Volts divided by 
ohms equal amperes. 



176 LABORATORY PROJECTS IN PHYSICS 

B. The Projection Lantern. Wire the terminals of a projection 
lantern in series with the ten-ampere rheostat and operate it. 

3. With respect to the center of the condensing lenses, how 
should the arc be placed ? 

4. Why are projection lantern carbons usually placed at right 
angles ? 

5. What kind of adjustments are provided for proper placing 
of the arc with respect to the condensing lenses ? 

6. What should be the position of the arc light with respect 
to the center of the slide and the center of the objective lens? If 
possible, move the arc light out of correct position and note the 
effect upon the image on the screen. 

C. Reference Work. Electricity Experimentally and Prac- 
tically Applied Ashe, Appendix. 

7. Why should a large carbon arc never be attached to an 
ordinary lamp socket? 

8. If the current is direct, which terminal of the line should be 
attached to the upper carbon? Why? 

9. Diagram a feed mechanism and rheostat with knife switch. 

10. How far apart should the carbons stand in operation? 

11. If the current is direct, which carbon burns faster? 

12. What would you expect to happen if no rheostat were used 
in the circuit? 



RHEOSTAT AND ELECTRICAL RESISTANCE 



177 



75. RHEOSTAT AND ELECTRICAL RESISTANCE 

To make a two-ampere resistance coil for the no-volt line. 

MATERIALS. No. 30 nichrome or nickel chromium resistance wire; 
iron or wooden rod of one-quarter inch diameter for winding coil ; projection 
lantern; large spool; wood frame; rheostat (10 amperes on no volts); 
ammeter. 

//<? vo/f e/ecfric current ou//et 
f? 






\ 



G/ass Tube 



fies/stance Co// 



\ 



fer-y 
Mounted 
FIG. 71. A coil of resistance wire with an ammeter in series. 

A. Resistance Wire. No. 30 nichrome wire has a rated resist- 
ance of six and two-tenths ohms per foot. By Ohm's Law (volts 
divided by ohms equal amperes) determine the number of ohms 
required to let two amperes flow through on the i zo-volt line. 

i. What length of No. 30 wire gives this amount of resistance? 
Have your determination of length approved by the instructor. 



i 7 8 



LABORATORY PROJECTS IN PHYSICS 



B. The Construction. Measure off this length and rewind it on an 
empty spool. (Caution. Keep this wire stretched when off the spool, 
as it is likely to become badly tangled.) Fasten the wire firmly at one 
end of the winding rod. Let your associate hold the spool while you 
wind the wire carefully on the rod. Each turn of the wire on the rod 
should be wound tight against the preceding turn and during the 
winding the wire should be stretched tight. When the winding is 
completed allow the coil to release and remove. Suspend this resist- 
ance coil on a ring stand from the two ends of a glass rod for testing. 

2. Connect the coil in series with an ammeter and note how 
many amperes it lets through when attached to the no- volt line. 

3. According to Ohm's Law, how 
many amperes flow would this resist- 
ance let through if attached to a 55- 
voltline? a 2 20- volt line? 

4. On the no- volt line, how many 
amperes would pass through two such 
coils connected in series? Diagram. 

5. How many amperes would flow 
through two such coils in parallel on 
the 1 10- volt line? Diagram. 

6. Make a diagram showing how 
coils of this type might be used for ob- 

FIG. 72. A variable rheostat, taining a io-anipere current. 

C. The Rheostat. Examine a large rheostat for the projection 
lantern. Some rheostats are made variable, for example, 10 to 
25 amperes. 

7. Indicate by diagram how the coils are arranged. 

8. Name two electrical instruments which use a rheostat. 

9. What would happen if one of these instruments were at- 
tached to the line current without the rheostat? Explain. 

10. Name four household utensils which employ resistance 
wires for generating heat. See Butler's Household Physics. 




SEWING MACHINE B 179 

76. SEWING MACHINE B 
To study the mechanical operation of a sewing machine. 

MATERIALS. One or more large sewing machines of the lock-stitch type ; 
screw driver ; oil can. 

References General Science, Barber ; General Science, Hodgdon ; 
Singer Manuals; Mechanics of the Sewing Machine; Chart Four 
Distinct Types of the Singer Sewing Machines, Singer Sewing 
Machine Co. 

A. The Mechanism. Remove the belt from the band wheel. 
Tilt back the machine head on its hinges so that you can observe 
the mechanism beneath. 

1. What make of machine are you studying? 

2. Is this machine a chain-stitch or a lock-stitch machine? 
Give a reason for your answer. 

3. Was the small machine used in Sewing Machine A, Singer 
No. 20, a lock-stitch or a chain-stitch machine? 

4. What are the four common types of machines for making 
lock stitches? See General Science, Barber, or Mechanics of the 
Sewing Machine. 

5. To which of the four types does this machine belong? 
Remove the face-plate on this machine. Locate the following 

parts : balance wheel, arm shaft, needle bar, thread take-up lever, 
presser bar, feed dog, stitch or feed regulator, bobbin holder, 
shaft or connecting rod which operates the bobbin, feed rock 
shaft. See General Science, Hodgdon. 

6. Name four essential moving parts of the machine. 

7. Name a single shaft by means of which all of these move- 
ments are controlled. 

8. The operation of a feed dog must consist of a combination of 
two motions, horizontal and vertical. How are these motions 
obtained ? 



i8o 



LABORATORY PROJECTS IN PHYSICS 




SEWING MACHINE B 



181 



9. Which of the two motions of the feed dog does the stitch 
regulator vary? 

10. How is the motion of the needle bar accomplished? 

11. How is the thread take-up operated? 

12. Explain how the arm shaft operates the bobbin holder. 

B. Types of Stitches. 

13. Diagram a series of stitches made by a chain-stitch machine. 
See General Science, Barber. 

14. Diagram a series of stitches made by a lock-stitch machine. 
For ordinary stitching, the upper and under threads of a lock- 
stitch seam should be locked midway between the upper and lower 
surfaces of the material. If the tension on the upper thread is 
too tight, or if that on the under thread is too loose, the threads 
will lock on the upper surface. 

15. Under what conditions of tension would the thread lock on 
the under surface of the material? 

16. How may the tension of the upper thread be adjusted? of 
the lower thread? 

C. Oiling. The importance of frequently oiling machines 
which involve considerable friction cannot be overestimated. 
The life of a sewing machine may be doubled by proper attention 
to this detail. Parts that move most need more frequent oiling. 

17. How many holes are provided for oiling the arm shaft? 

1 8. How would you oil the needle-bar mechanism? 

19. How many bearings should be oiled underneath the head? 



182 LABORATORY PROJECTS IN PHYSICS 

77. THE STEAM ENGINE 

To operate a steam engine and study its action. 

MATERIALS. Boiler; engine; tubing, small demonstration model. 

NOTE. The pressure cooker may be fitted with an outlet and stop-cock and 
used as a substitute for a boiler. To avoid ruining the pressure cooker by 
boiling it dry, place three quarts of water in it and record the starting time. 
Do not heat longer than twenty minutes without refilling it. 

A. Filling and Heating the Boiler. Examine the tubes of the 
boiler before heating it. (Caution. Never build a fire under a 
boiler unless you have water in it, otherwise the boiler may be ruined. 
In operating, never allow the water-level to drop as low as the bot- 
tom of the water gauge. In this experiment do not let the pressure 
gauge rise above thirty pounds per square inch.} The principal parts 
of the boiler are : boiler tubes, firebox, ash pit, grates, water 
gauge, steam gauge, and safety valve. 

Fill the boiler three-fourths full and heat by means of the gas- 
burner in the firebox. Turn gas on full. Before starting the 
engine, oil all bearings. 

1. What automatic protection have boilers against accumu- 
lating an excessively high pressure ? 

2. When the pressure gauge of a boiler registers 100 Ibs. per 
square inch, how hot is the water in the boiler? Refer to a table 
of pressures and temperatures. See Barber's General Science. 

3. At what temperature does water boil under 75 Ibs. per 
square inch gauge pressure? 

In the boiler of a locomotive the pressure is about 200 Ibs. per 
square inch, and the boiling point is about 390 F. On the top 
of Mt. Blanc, three and one-half miles above sea level, the pressure 
is about 7! Ibs. lower than the pressure at sea level, and the boiling 
point is 185 F. 

4. Draw a section of an upright (fire tube) boiler. See Barber's 
General Science. 



THE STEAM ENGINE 




FIG. 74. A boiler and steam engine. 



1 84 LABORATORY PROJECTS IN PHYSICS 

5. Draw a section of a water tube boiler (high pressure). See 
Black and Davis. 

6. What kind of boiler is used in this experiment? 

7. What is the purpose of a thick covering on the outside of a 
boiler ? 

8. Draw a safety valve (lever type). See Black and Davis. 

9. What per cent of the heat of the coal is utilized by an 
ordinary engine boiler? See Black and Davis Efficiency. 

B. The Operation of the Engine. Examine the small demon- 
stration model and observe how the slide valve directs steam first 
to one side of the piston, then to the other. Open the valve be- 
tween the boiler and the engine. The engine should run, provided 
the steam pressure is sufficient. 

10. Diagram the steam-chest and cylinder, showing the position 
of the slide valve and piston. See Millikan, Gale and Pyle. 

The slide valve is usually set so that the admission of the steam 
takes place a fraction of a second before the piston reaches the end 
of the stroke, in order that the space may be filled with steam 
when the return stroke begins. This is called " lead." The 
same thing occurs in regard to the explosion in the cylinder of 
the gas engine. Furthermore, it has been found more economical 
to cut off the entrance of steam before the stroke is completed. 
Steam ordinarily enters during only one- third to one-half of the 
length of the stroke. After the cut-off, the expansive force of the 
steam exerts some pressure during the remainder of the stroke. 

11. Name five important parts of an ordinary steam engine. 

12. On what principle does the governor work? How does 
the governor gradually shut off the flow of steam as its speed 
increases? See Hoadley. 

13. What per cent of the heat of the coal is converted into 
mechanical energy in a simple type of steam engine? See Black 
and Davis Efficiency. 

14. Outline a brief history of the steam engine. See Barber. 






TELEPHONE A 185 

78. TELEPHONE A 
To study the operation of a telephone. 

MATERIALS. Three telephone receivers, one to be opened ; two micro- 
phone transmitters ; two dry cells ; wires extending from one room to another ; 
clock ; two thin copper plates about an inch and a half in diameter ; bottle of 
carbon granules, made from a crushed projection lamp carbon. (Part of the 
apparatus for this experiment must be obtained from the instructor.) 

A. Telephone Receivers. Test each receiver by touching the 
wires to the terminals of a dry cell to see if they are in working 
condition. The diaphragm should sound. 

1. What happens to the diaphragm when the battery current 
passes through the receiver ? 

Attach one of the receiving instruments to the binding posts at 
each end qf the line by means of wires (without batteries). Make 
all wire connections tight. Let your associate say " Hello ! " 
into one receiver while you hold the other to your ear, and vice 
versa. By speaking against the diaphragm of one instrument, 
causing it to vibrate, you generated minute electrical pulses which 
in turn pulled the diaphragm at the other end of the line and 
reproduced the sound. Unscrew the cover from the large end of 
the receiver labeled " To be opened," and observe the mechanism. 
'(Caution. Do not break the delicate wires.) 

2. Diagram a simple telephone system consisting of two 
receivers and two wires. See Millikan, Gale and Pyle. 

The principal parts of a receiver are : permanent magnet, coil 
of wire, and diaphragm. 

3. Diagram a typical receiver. See Millikan, Gale and 
Pyle. 

4. When the diaphragm is touched against the end of the 
magnet, why does it not fall off? 

5. When the diaphragm is in position it should not quite 
touch the end of the magnet. What happens to this diaphragm 



i86 



LABORATORY PROJECTS IN PHYSICS 



when you speak against it? When the instrument is used in this 
way it is a generator of minute electric current pulses. 

6. Why is it incorrect to say that the sound passes over the 
wires ? What does pass over the wires ? 

7. Explain what happens at the other receiver if you tap the 
diaphragm slightly with the point of a pencil. 



A 



Receiver 



Receiver 



Receiver 




Copper p/afes 
w/th carbon 
Z)ry Oe//s granules between 



Receiver . 



C 




Transmitter 



Dry Ceffs 



NJ 

fc 

Trar 
fa 


, 


Z}ry Ce//s 

? i (T^{^ 1 


J 


IP 
=0 

a^7C/ 

r 


=8 

ismitt 
*ce/vi 


\ 

in 

litter 
ceive 


e/~ and ^} Transn 
?r Re 



FIG. 75. Wiring for the study of telephone transmitters and receivers. 

B. The Microphone Transmitter. The first telephones used 
two receivers as above, with batteries, but they were not satis- 
factory for very great distances because the current pulses are so 
small. The microphone has aided in making longer distance 
telephoning possible because it causes pulses of greater magnitude. 
The use of the induction coil will be studied in Telephone B. 

Make a microphone transmitter as follows : Attach one terminal 
of the dry cells to a copper plate and the other terminal to the 
line. Attach the other copper plate to the second terminal of the 
line. Place a half dozen small granules of carbon on the one plate 



TELEPHONE B 187 

and carefully lay the other copper plate on the carbon granules 
so that the granules completely separate the two plates. Attach 
a receiver at the other end of the line. 

8. Touch the upper plate with the end of a strip of paper. 
This touch should be audible in the receiver at the other end of 
the line. Explain. 

9. Place an alarm clock in a horizontal position, face up, 
under the plates, so that the plates with carbon granules rest upon 
the clock. You should hear the clock tick in the receiver at the 
other end of the line. Explain. 

10. Attach the microphone transmitter and two dry cells at 
one end and a receiver at the other. Stand the microphone trans- 
mitter on a clock, or speak into it. Can you use the microphone 
transmitter as a receiver ? Explain. 

11. Connect a transmitter and a receiver in series at one end, 
and a transmitter, a receiver, and two dry cells in series at the 
other end. Speak through this system. Diagram it. 

79. TELEPHONE B 

To study the operation of a two-party telephone. 

MATERIALS. Two telephone outfits; magneto generator; screwdriver. 
(Part of the apparatus for this experiment must be obtained from the 
instructor.) 

A. Attaching the Telephones. Two telephone outfits will be 
found in the cabinet. Attach them to the hooks at the terminals 
of the laboratory telephone lines. The two terminals at the top 
of each telephone are to be connected by wires to the terminals 
of the line. The two terminals at the bottom of each instrument 
should be connected to a set of two dry cells. Make all wires tight 
to insure contact. 

i. Diagram a simple local battery telephone system with pri- 
mary and secondary circuits, including receivers, transmitters, 
batteries, and induction coils. See Millikan, Gale and Pyle. 



i88 



LABORATORY PROJECTS IN PHYSICS 



B. The Induction Coil. For longer distances it is necessary to 
use, in addition to the microphone transmitter, an induction coil. 
This is a small iron bar surrounded by two separate coils, one of 
few turns and one of several hundred turns. It is a small trans- 
former. The transmitter current pulses go through the coil of 
few turns and back to the dry cells and transmitter. The coil of 





Dry Ce//s F IG , 7 6. A two-party telephone system. Dry Ce//s 

many turns changes the three-volt current of the transmitter 
circuit to a higher voltage current for long distance. 

C. The Magneto Generator. Attach a magneto generator and 
use it to ring up the other party. 

D. Study of the Wiring Circuits. 

2. Make a careful diagram of the wiring of the telephone as 
shown in the illustration. Note that a dotted line and a full line 



Transm/tter 




J 




o 

FIG. 77. Wiring diagram for a two-party telephone instrument. 
189 



1 90 LABORATORY PROJECTS IN PHYSICS 

represent the two possible positions of the hook, and also of the push 
button. You will find one of the instruments open so that you 
can observe the mechanism. 

3. Indicate by the lettering, the path which the bell current 
takes in your instrument when the party at the other end of the 
line rings you up. Assume that the current enters at B. 

4. Indicate the path of the current through your instrument 
when you push the button and ring up the other party. Begin at 
your battery. 

5. Can the other party ring you up if your dry cells are ex- 
hausted or disconnected from the line ? 

6. When the hook is up, indicate by the lettering the circuit 
which operates the transmitter and the primary coil of the induc- 
tion coil. Begin at the dry cells. The magnetism produced 
by the current pulses through this coil induces a high voltage 
current in the secondary coil. This secondary current goes to the 
other instrument, operating the receiver. 

7. Beginning at the secondary coil of the induction coil, in- 
dicate by the lettering how the secondary circuit passes through 
your instrument when you are telephoning. 

8. If your receiver is off the hook can the other party ring you 
up ? Explain. 

9. If your hook is held down can you speak to the other party? 
Explain. 

10. If your hook is held down can you hear the other party? 
Explain. 

80. THE TELESCOPE 
To study the astronomical telescope. 

MATERIALS. Large reading glass lens; lens of short focal length; 
ring stands. (Part of the apparatus for this experiment must be obtained from 
the instructor.) 

A. Lens Images. Make a careful preliminary drawing of the 
image of a gas flame as it is produced on a cardboard screen by 



THE TELESCOPE IQI 

a simple convex lens. Trace the paths of light rays from two 
different points on the flame as they pass through the lens to il- 
luminate the screen. Follow three light rays from each of these 
points on the object through the lens to their focus on the screen. 
One of each three rays should pass through the optical center of 
the lens, and the other two should pass on either side of the opti- 
cal center. Have this drawing approved. 

(Caution. Do not touch the surface of an expensive lens with 
your fingers, or with any other object.} In making measurements 
measure approximately from the center of the lens. 

1 . Under what conditions is the image equal to the object in 
size? 

2. Under what conditions is the image smaller than the object? 
Larger ? 

3. As an image is made larger, how is its brightness affected? 

4. How do the sizes of the object and the image compare with 
their distances from the optical center of the lens? 

5. If the image is twice as far from the lens as the object, how 
do their sizes compare? 

B. Telescope Lenses may be represented by a large lens of long 
focal length and a small lens of short focal length. 

The principal focus is the point of focus for parallel rays, for 
example, the rays of the sun. The focal length is the distance 
of the principal focus from the optical center of the lens. 

6. Find the focal length of the two telescope lenses by one of 
the following methods : 

a. Hold the lens in the path of the direct rays of the sun, and 
measure the focal distance directly. Use only the central region 
of the lens by holding a piece of cardboard with a one-inch hole 
in front of the lens. 

b. Focus the lens on a distant object (500 feet or more away). 
Light rays from this object will be approximately parallel and 
the image of the distant object may be considered at the prin- 



IQ2 



LABORATORY PROJECTS IN PHYSICS 




JRet/na 



JZyep/ece 
Lens Lens 



I 

\ Objective Lens 



Object appears 
to 6e here. 



Ob/'ect 



f/ "*Sr* to 6e here. 

FIG. 78. A telescope with diagram showing how the light rays are refracted, producing 
an enlarged image on the retina. 



THE TELESCOPE 



193 



cipal focus. When the object is in sharpest focus, measure the 
distance from the optical center. 

C. The Astronomical Telescope. In the astronomical telescope 
the degree of enlargement depends upon the power of the eyepiece 
and the focal length of the objective. An objective with a long 
focal length gives a larger image than one with a short focal 
length. The size of a lens image is proportional to its focal 
length. An objective of large diameter is preferable to a small 
one because it collects more light from the object, and thereby 
makes a more brilliant image. The more brilliant the image, 
the higher it may be magnified by the eyepiece. 

Set the large objective lens in position at one end of the labor- 
atory, and, with a cardboard screen behind it, get the image of a 
window located at the other end of the room. 

7. What is the distance of this image from the center of the lens? 




Eyepiece 

fief/na 2,ens Lens Object appears 

Jmge to be here. 



Objective 
ens 



Object 



FIG. 79. A terrestrial telescope. The two lenses between the objective and the eye- 
piece cause the object to appear upright. 

Now remove the card and bring the eyepiece lens into position 
near the point of focus. Look into the eyepiece and you should 
be able to see the image enlarged. 

8. Should the eyepiece be nearer the objective lens than the 
image in question 7, or farther away? 

9. Make a careful diagram of the path of light rays from the 
object through both lenses of the telescope. 



IQ4 LABORATORY PROJECTS IN PHYSICS 

Si. THE THERMOMETER 

To make a thermometer. 

MATERIALS. Thermometer tubing one millimeter bore; atomizer 
bulb ; kerosene in small bottle ; two Bunsen burners giving sufficient heat to 
readily melt glass tube ; beaker and stand for boiling water ; glass funnel and 
rubber connection. 

A. Making Thermometer Bulbs. Adjust the Bunsen burner so 
that it gives the maximum heat (colorless or blue flame). The 
Bunsen burner should be of large size. Have the Bunsen flame 
inspected by the instructor before proceeding further. As a pre- 
liminary exercise attach an atomizer bulb to one end of a piece 
of ordinary laboratory glass tubing (large bore of three or four 
millimeters diameter), and heat the other end in the flame till it 
softens and seals. (NOTE. Keep revolving the tube in the flame 
to avoid bending. Hold the tube in the flame steady by resting 
your elbow on the table. Do not allow it to seal more than a 
quarter inch from the end.) When the end of the tube is well 
softened remove quickly from the flame, hold in a vertical position 
and compress the bulb firmly, but cautiously. When the glass 
bulb is as large in diameter as a dime, hold the atomizer bulb 
steady for a moment till the glass hardens. The glass bulb will 
collapse if the rubber bulb is released too soon. If the bulb is 
imperfect, or too large, cut the tube off and begin the operation 
again. Have the preliminary bulb approved by the instructor. 
He will then give you a piece of thermometer tubing. 

B. Attach the atomizer bulb to the piece of small bore ther- 
mometer tubing. Make connections air tight by wrapping with 
heavy thread. Proceed as before and make a bulb as large in di- 
ameter as a dime. (Caution. Heat gently at first to avoid crack- 
ing the thick wall tubing.) 

C. Filling the Thermometer with Expansion Liquid. First 
remove the rubber bulb and attach a funnel by means of a short, 



THE THERMOMETER IQ5 

rubber-tube connection. Pour into the neck of the funnel just 
enough kerosene to fill the thermometer. With liquid in the 
funnel hold the empty bulb near a flame (not in the flame) till it 
becomes warm. Allow it to cool and as the heated air in the bulb 
contracts, liquid will pass into the bulb, filling it perhaps one- 
fourth full. Now heat this liquid in the bulb cautiously till it 
begins to boil. This boiling drives out the remaining air and on 
cooling it will fill completely. When it is completely filled, place 
the thermometer with funnel attached in a beaker of boiling water. 
When the liquid in the thermometer reaches the temperature of 
boiling water, the funnel may be removed. (Caution. Pour 
excess kerosene carefully into an evaporating dish.} A bubble may 
be removed from the bulb by tapping with the finger so that it 
rises to the top in small bubbles, or by shaking up and down very 
forcefully. 

NOTE. The kerosene may be dyed red with an oil soluble dye. This 
involves danger of soiling clothing in case the bulb breaks. 

D. Sealing the Upper End. In a beaker of boiling water the 
top of the liquid column should stand about an inch and a half 
from the end. If the liquid rises to the extreme top, hold it cau- 
tiously over a flame till a drop is forced out. Now place it in 
water at faucet temperature. The column should then stand at 
about one-third the height of the tube. If cracked ice or snow is 
available, observe where the column stands at freezing tempera- 
ture. For sealing, place the bulb in boiling water. In boiling 
water the liquid column should stand about an inch and a half 
from the top. Holding a Bunsen burner in your hand, heat the 
end of the thermometer (heat gently at first) till it seals. Turn it 
while sealing to prevent bending. If bubbles reappear in the bulb 
when it contracts, they may be removed as suggested above. 
This thermometer should be mounted on a board, or card, on 
which a scale has been marked by comparison with a correct 
thermometer. In this form it may be used as a room ther- 
mometer. Mark the boiling point with a file when the bulb is 



196 



LABORATORY PROJECTS IN PHYSICS 




Heating the g /ass tube to cause 
it to soften and seat the end for 
a distance of one quarter inch. 



V Punnet 

Kerosene 



Rubber connection 




ff /owing the g/ass bulb. 



Leve/ of 
Thermometer //qu/d 



fi//ing the bu/b 
with kerosene. 




Boi/ing 
Water 



Sea/ing the upper end 
the bulb in bo/7/ng wate/ 

FIG. 80. Making a thermometer. 



THE THERMOMETER 1 97 

held in a beaker of boiling water. Mark the freezing point when 
the bulb stands in melting ice or snow. 

1. Why should a thermometer be sealed when the liquid is at 
the top? 

2. Glass expands at a slower rate than kerosene. If they ex- 
panded at the same rate, what would be the result? 

3. Why are thermometers made with cylindrical bulbs instead 
of spherical ones ? Which form of bulb has the greater surface ? 

4. How is expansion utilized in the filling of the thermometer ? 

5. How is vaporization utilized in the filling of the thermometer ? 

6. How is atmospheric pressure utilized in the filling of the 
thermometer ? 

7. Why does a bubble of air in the column become larger when 
the upper end is sealed and the thermometer cools? 

E. A Mercury Thermometer may be made in a similar manner. 
Mercury is the best liquid for registering high temperatures because 
it has a high boiling point, 357 C. or 675 F. The freezing point 
of mercury is 39 C. Alcohol is best for low temperatures be- 
cause it freezes at 130 C. Mercury affords the largest range on 
both sides of the ordinary temperatures. 

F. References. 

a. General Science Hodgdon. 

8. Diagram the three types of thermometer scales indicating 
the temperatures of melting ice and of boiling water. 

9. What are the temperatures of the following in Fahrenheit 
and Centigrade : the sun, an arc lamp, melting tungsten, melting 
cast iron, melting aluminum, liquid air, lowest temperature reached? 

10. What are the temperatures of the following : baking bread, 
pasteurizing milk, high fever, normal body, incubator, room 
temperature, household refrigerator, danger of frost? 

b. Weather Jameson. 

11. Explain briefly what is meant by maximum thermometer, 
minimum thermometer, clinical thermometer. 



198 LABORATORY PROJECTS IN PHYSICS 

82. THE VACUUM CLEANER 
Centrifugal Fan Type. 

To study the construction of a vacuum cleaner and measure 
its suction, fan speed, and current consumption. 

MATERIALS. Vacuum cleaner; rubber stoppers; tubing; U-tube; 
water gauge; speed indicator; rule; ammeter; rug; 3o-lb. spring balance; 
screw driver. (Part of the apparatus for this experiment must be obtained 
from the instructor.) 

A . Construction. This vacuum cleaner operates by means of a 
centrifugal fan attached to a high-speed electric motor. Observe 
the following parts: cleaning tool, fan housing, motor housing, 
fan outlet, and bag. With a screw driver open the fan housing. 
(Caution. Handle the apparatus very carefully, especially in taking 
apart. Screws and threads may be easily ruined. Do not lose the 
parts.) 

1. What is the diameter of the fan ? 

2. How many vanes has the fan? 

3. What is the width of the vanes? 

4. Are the vanes straight or curved ? 

5. Measure the length and width of the cleaning tool opening 
in inches. 

6. Measure the inside diameter of the outlet from the fan at 
the point where it attaches to the bag. 

7. How many places for oiling has this apparatus? The life 
of a high-speed motor may be reduced one-half by failure to 
properly oil the bearings. Unless the bearings are provided with 
special oil cups, they should be oiled each time the machine is 
used. 

8. Is the motor shaft in vertical or horizontal position ? Hori- 
zontal is preferable because the weight then rests on two bearings 
instead of one. 



THE VACUUM CLEANER 



199 



9. Of what material are the fan and motor housing made? 
What are some advantages of aluminum? 

10. What does the entire machine weigh in pounds? What 
are some disadvantages of large, heavy machines? 







FIG. 81. A vacuum cleaner with manometer attached for measuring its suction in 
inches of water column. 

B. Speed of the Fan. (Do not make this determination with- 
out the assistance of the instructor.) The machine should be 
placed on the rug in actual working condition. The speed indi- 
cator is held firmly against the end of the motor shaft. Count 
the number of revolutions of the dial in fifteen seconds and cal- 
culate the rate per minute. 



200 LABORATORY PROJECTS IN PHYSICS 

11. How many revolutions does the motor make while the 
dial of the speed indicator makes one revolution (gear ratio)? 

12. Record the speed of the fan per minute. 

C. Test of Fan Suction. Fill the manometer tube half full of 
water. Make this test with all inlets completely closed. Close 
cleaning tool opening. Attach the manometer to the special 
attachment opening by means of a large rubber stopper and 
rubber tubing. Turn on the current and measure the difference 
between the water levels on the two sides in inches. This is the 
suction in inches of water. 

13. What is the maximum suction with bag removed? 

14. What is the maximum suction with bag attached? 

D. Cost of Operation. With the instructor's assistance, attach 
an ammeter and measure the current in amperes. 

15. Find the current consumption in watts. See line volt- 
meter for voltage. (Volts times amperes equal watts.) 

1 6. Calculate the cost of operation per hour at ten cents per 
kilowatt hour. 

83. WATER HEATER GAS 
Thermal Efficiency. Kitchen Tank Type. 

To determine what part of the total B.T.U. given out by the 
combustion of a quantity of gas enters the coils of a kitchen 
tank water heater in heating water from faucet temperature 
to 110 Fahrenheit. 

MATERIALS. Gas meter; water heater; two two-hole rubber stoppers to 
fit water inlet and outlet of the water heater ; two Fahrenheit thermometers, 
one in each of the two stoppers ; rubber tubing ; short glass tubes for con- 
nections at stoppers ; screw clamps ; faucet stopper ; gallon measure. 

A. Attaching the Water Heater. Connect a tube from the gas 
cock to the inlet side of the gas meter. Connect a tube contain- 



WATER HEATER -GAS 



201 



ing a screw clamp from the outlet side of the meter to the water 
heater. (Caution. Allow a quarter of a cubic foot of gas to flow 
through the meter before lighting.) Attach the water tube to the 
faucet by means of the rubber tube attachment and send the water 
through the heater coil from 
the bottom upward. Record the 
entering temperature. (Caution. 
Do not heat the coil when no water 
is flowing through it. Before be- 
ginning the experiment the water 
should be allowed to run till its 
temperature becomes approximately 
constant.) 

B. The Test. When the faucet 
temperature becomes nearly con- 
stant, light the burner and turn 
it on full. (Caution. Avoid an 
explosion by holding a lighted match 
over the burner before turning on the 
gas.) Adjust the flow of water by 
means of the faucet so that trie 
temperature of the outlet ther- 
mometer remains as nearly as 

possible at IIO (temperature of FI G- 82. A sectional view of a gas water- 
i. j. -L J.-L\ TITU .LI.' j- heater showing the heating coil. 

a hot bath). When this condi- 
tion of adjustment is reached, place a gallon measure under the 
outlet pipe, at the same time beginning the meter readings. 
When one gallon of water has passed through the heater, note on 
the gas meter how many cubic feet of gas were consumed. Record 
thermometer readings on both sides of the heater each minute of 
the experiment. Average the readings for each thermometer. 
The B.T.U. taken up by the water in passing through the coils is 
found by multiplying the amount of water in pounds heated by 
the difference in temperature on the two thermometers. One 




202 



LABORA 



N PHYSICS 



gallon of water weighs eight and three-tenths pounds. Make at 
least two tests and 'see if they agree. 

1. How much heat in B.T.U. did the water receive? 

2. How much gas in cubic feet was consumed? 




FIG. 83. A gas water heater attached to a kitchen hot water tank. The kitchen 
range is also attached to the same tank. 

3. How much heat in B.T.U. did this amount of gas repre- 
sent? (One cubic foot gives out six hundred B.T.U.) 

4. What percentage of the total heat produced by the gas did 
the water receive? Thermal efficiency equals heat received by 
the water divided by heat of combustion of the gas. (Question 3.) 



F 

MOTOR B 2O$ 

5. Diagram a gas water heater connected to a kitchen tank. 
See Butler's Household Physics. 

6. Diagram a kitchen tank attached to a range. See Mechanics 
of the Household Keene. 

7. What is a waterback? 

Instantaneous Gas Water Heater. These heaters are made 
very large for supplying hot water faucets directly without the 
use of a storage tank. The gas is turned on automatically as a re- 
sult of opening the faucet. This is accomplished by means of a 
special mechanism which is operated by the water pressure. 
When the faucet is closed the gas is automatically shut off. In 
these heaters a small pilot light burns continuously for the pur- 
pose of lighting the burners. On account of its large size an 
instantaneous automatic heater is expensive but it is at the same 
time a very convenient and efficient source of hot water. 

A hot water tank may be connected to two sources of hot water 
supply for example a kitchen range and a gas heater. In this 
arrangement the gas heater is used when the range is not in 
operation. It is a common practice to install hot water tanks in 
the basement and to connect them to the furnace and to a gas 
heater. The furnace supplies the heat in winter and the gas 
heater in summer. 

84. WATER MOTOR B 
Brake Horse Power and Efficiency. 

To determine the horse power of a faucet water motor. 

MATERIALS. Water motor with Bourdon pressure gauge attached ; two 
spring balances with heavy cord; speed indicator; ring stand for holding 
balances. 



A. Operating the Motor. Attach the motor to the faucet, and 
turn on the water. These motors are made to operate with a 
comparatively small flow of water under high pressure. For effi- 



2O4 



LABORATORY PROJECTS IN PHYSICS 






cient work the pressure should not be less than thirty pounds per 
square inch. Remove the motor from the faucets and look into 
the water outlet and observe the wheel. Note the vanes or paddles 

which are pushed around 
by the impact of the 
stream of water. 

1. Attach the motor to 
the faucet and measure 
the water pressure, when 
the motor is running. 

2. What height of water 
column in feet is required 
to produce this pressure 
per square inch ? (A water 
column two and three- 
tenths feet high exerts a 
pressure of one pound per 
square inch.) 

B. The Power of the 
Water Motor. Operate 
the water motor, and with 
a speed indicator held 
against the end of the 
motor-shaft, measure the 
number of revolutions per 
minute. One revolution 
of the indicator dial equals 
one hundred revolutions 

of the motor-shaft. Hold the indicator firmly enough to prevent 

slipping, but not so firmly as to reduce the speed. 

3. With the second hand of a clock, count the number of revo- 
lutions per minute when the motor is running without load. 
Suspend two spring-balances from a ring stand as shown in the 




FIG. 84. Apparatus for measuring the horse 
power of a water motor. 



WATER MOTOR B 

diagram, with heavy cord passing around the water-motor pulley. 
Note that the speed of the motor decreases as the tension of the 
balances, is increased, producing greater friction on the motor 
pulley. If the tension is increased enough, the motor will be com- 
pletely stalled. Note that as friction is applied by increasing the 
tension on the balances as the motor runs, one balance will be 
pulled more than the other. The pull exerted by the motor is 
the difference between the readings on the two balances. 

4. Make at least five measurements of the pounds pull and 
the speed per minute, beginning with a very slight pull and in- 
creasing with each measurement so that the last measurement is 
made with enough tension to cause the motor to run at a com- 
paratively slow speed. Multiply the pull in each case by the 
corresponding speed per minute. One of the products should 
represent the maximum. If the last product is the greatest, you 
have not made the tension great enough, and more readings should 
be taken. In a series of five products the third or fourth should 
be greatest. Make a table showing the data for these five or more 
measurements. 

5. From the pounds pull and the revolutions per minute of the 
maximum, calculate the work done per minute. (Pounds times 
circumference of pulley in feet times speed per minute.) 

6. From the result in question 5, what is the maximum horse 
power of this motor? (Foot pounds per minute divided by 

33>oo.) 

7. Refer to Water Motor A, and calculate the efficiency of this 
motor. (Efficiency equals horse power output divided by cal- 
culated horse power input, or work out divided by work in.) 



206 LABORATORY PROJECTS IN PHYSICS 

85. WIRELESS A 
(Simple Outfit) 

To construct and operate a simple wireless sending and receiving 

system. 

MATERIALS. The Sending Apparatus. Copper sending aerial wire 
reaching from one side of the room to the other ; induction coil ; four dry cells ; 
telegraph transmitter ; connecting wires. (Part of the apparatus for this ex- 
periment must be obtained from the instructor.) 

The Receiving Apparatus. Copper receiving aerial wire of same length as the 
sending aerial ; simple crystal detector ; 1000 ohm telephone receiver. 

NOTE. You will find a sending aerial wire suspended across one end of 
the laboratory. The receiving aerial is similarly located at the opposite 
end of the room. Connect the receiving apparatus at one end and the 
sending apparatus at the other. 

A . Sending Instrument, Induction Coil. (Caution. Keep 
away from the secondary terminals of an induction coil when it is 
connected to a battery, as the secondary current is dangerous.) First 
set up the induction coil at the sending end. Before attaching 
the dry cells connect a short wire to one of the secondary termi- 
nals of the induction coil and bend it into position so that it 
stands about one-quarter inch from the other secondary terminal. 
Connect four dry cells to the primary circuit, including in the 
circuit a telegraph key for making and breaking the flow of current 
into the induction coil. Now operate the induction coil by means 
of the telegraph key and note the high voltage discharge across the 
quarter-inch spark-gap. A single spark consists of many oscilla- 
tions vibrating at the rate of about a million per second back and 
forth across this quarter-inch gap. Now connect a wire between 
one end of the aerial and one of the secondary posts of the induc- 
tion coil. From the other secondary post of the induction coil, 
lead a wire to the ground by attaching it to a gas pipe or water 
pipe. This completes a simple sending instrument. 



WIRELESS A 



207 



1. Diagram a simple sending instrument. See Black and 
Davis. 

2. Diagram an induction coil. See Millikan, Gale and Pyle or 
Carhart and Chute. 

3. Of what material is the core made? 

4. What causes the vibrator or interrupter to move toward the 
core? 

5. What causes it to come back ? 

6. What effect has the vibrator upon the current which passes 
through the primary coil of the induction coil ? 

7. Of what material is a condenser made? 



Aer-/a/ 



Pr/mary Term/na/s 



L 



r r 


ir 


ir 


ir 












JCey 



FIG. 85. Simple wireless sending apparatus. 



To Ground, 
Gas or- 
WaterPfie. 



8. How does the condenser affect the sparking at the vibrator? 
Otherwise the magnetism of the core would not break quickly and 
the voltage in the secondary would be much less. 



208 



LABORATORY PROJECTS IN PHYSICS 



I I ) I t- 




Z>efector Stand 



/OOO Ohm 

Te/ephone Receiver 
w/th Head-band. 



To Ground, 
Gas or Water P/pe. 

FIG. 86. Simple wireless receiving apparatus. 



Aer/'a/ 



Crysta/ 
Detector 



o 



/OOO Ohm 
Te/ephone 
II fiece/'ver 



. Ground 

FIG. 87. Diagram of the detector type of receiving apparatus. 



WIRELESS A 209 

B. Receiving Instrument, Crystal Detector Type. Connect 
one wire from the aerial to one post of the detector. Connect a 
second wire from the second post of the detector to the ground, gas 
pipe or water pipe. Attach the telephone receiver to the same 
two detector posts. A wireless wave sets up an oscillation be- 
tween the aerial and the ground, which affects the telephone 
receiver. Contact at the crystal should be as light as possible. 
A faint click should be heard in the receiver when a spark sets 
up an oscillation on the sending wire. The oscillation on the 
receiving wire is a miniature of the sending oscillation (about a 
million alternations per second). 

9. What effect has the crystal upon these rapidly alternating 
surges? Refer to texts. 

10. Does all of the oscillating current pass through the tele- 
phone receiver? Explain. 

11. Why is it necessary to have direct current pulses in the 
telephone receiver? 

C. Receiving Instrument, Coherer Type. The instrument 
first used by Marconi for detecting wireless waves was of the 
coherer type. See Carhart and Chute, or The Ontario Physics. 
Connect a coherer in series with an electric bell and a single dry 
cell. Attach the aerial wire to one side of the coherer and the 
ground wire to the other side. Compress the filings slightly in 
the coherer, till the bell rings, then tap the glass tube with a pencil, 
and when the filings are shaken the bell should just stop ringing. 
Now operate the sending instrument and the bell should ring 
again. This experiment requires a bell which operates with very 
little current. The coherer must be set so that the bell is just at 
the point of ringing. 

12. Explain the operation of the coherer in ringing the bell. 

D. Wireless Waves. The wireless waves are usually from 
400 to 9000 feet long. They travel at the speed of light, 186,000 
miles per second. 

p 



210 LABORATORY PROJECTS IN. PHYSICS 

E. The Detector. The oscillating surges caused in a receiving 
aerial by the wireless waves cannot be used to operate a telephone 
receiver without some means of changing it to a direct current. 
Certain minerals and crystals permit current to flow through 
them in one direction more readily than in the other. This gives 
the effect of a direct current, since the flow in the opposing direction 
is reduced. Among the materials best suited for this purpose 
are silicon, galena, and iron pyrites. The crystal is so placed that 
the aerial current must pass through it on its way to the ground. 
The telephone receiver is shunted across the detector. Thus the 
crystal serves as a form of resistance for oscillations in one' direc- 
tion. This tends to send these oscillations across by way of the 
receiver. By using a tuner and a condenser in connection with the 
simple detector, it is not difficult to receive messages from distant 
points. A simple coherer as described in A cannot be used for 
signaling a much greater distance than a mile. 

F. The Aerial Wires. For a small outfit the aerials ordinarily 
are from 50 to 1 50 feet long. They should be suspended as far as 
possible from any tall objects. Care should be taken to insulate 
them from other objects. 

In order to avoid confusion of signals, laws have been enacted 
governing the size of sending apparatus for amateurs. 

86. WIRELESS B 

To wire and operate sending and receiving apparatus with 
tuning coils and condensers. 

MATERIALS. Sending apparatus: Aerial; induction coil; sending trans- 
former (helix) ; condenser, 4 dry cells ; key. 

Receiving apparatus: Aerial; slide tuner; detector; 1000 ohm telephone 
receiver ; fixed condenser ; variable condenser ; receiving transformer. (Part of 
the apparatus for this experiment must be obtained from the instructor.) 

A. Wiring Diagrams. Make careful copies of the wiring dia- 
grams for sending and receiving instruments as found below. Note 



4 WIRELESS B 



211 



Aer,af 




Dry Ce//s 



Aerta/ 



Dry Ce//s 



Aeriaf 



Co// 



Ground 




Ground 




Sending Transformer 
or ffe/ix 






A Dry Ce//s Ground 

FIG. 88. Wiring for wireless sending apparatus. 



212 



LABORATORY PROJECTS IN .PHYSICS 



Detector 




/OOO OAm 

Te/ephone 

Receiver 




Ground 



FIG. 89. Wiring for wireless receiving apparatus. 



WIRELESS B 213 

that the diagrams begin with the simplest wiring and proceed to the 
more complicated apparatus for selective tuning and greater distance. 
Set up the necessary instruments and operate a simple wireless 
with a crystal detector for the receiving instrument. 

B. Tuning. If two pianos are in the same room and. the dampers 
raised, when one string is struck a similar string in the second 
piano will be set in vibration (sympathetic vibration) by the air 
waves, because this second string is in tune with the first. In the 
simple wireless outfit, if the receiving aerial is of exactly the same 
length and size as the sending aerial, they are said to be in tune 
and they will operate successfully. If, however, the sending 
aerial should be two hundred feet long, and the receiving aerial 
should be fifty feet long, they are not in tune and the operation 
will not be as efficient. In this case by adding a coil of wire called 
a tuner, to the short receiving aerial, it is possible to make 
these wires operate similarly to wires of the same actual length. 
The tuner contains a slide by means of which the number of turns 
in the coil may be varied. Tuning coils and condensers are used 
to change the inductance and capacity of oscillating circuits for 
the purpose of making one circuit oscillate in tune with another. 
The receiving aerial should be in tune with the sending aerial and 
the circuit through the telephone receiver and detector should be 
in tune with the oscillation on the receiving aerial. When a con- 
denser of proper size is used in the secondary circuit of the tuner 
of the receiving instrument, the oscillations which are induced 
in the secondary will be made stronger, thus affecting the receiver 
more intensely. A very common arrangement is to place a 
variable condenser in parallel with the secondary winding and a 
fixed condenser in series. In general these condensers are small. 
Their size is determined by the inductance and capacity required 
for the secondary circuit. 

i. What is the wave length of one of these aerials when used 
as a simple instrument? (The wave length of a simple aerial is 



214 LABORATORY PROJECTS IN PHYSICS 

approximately four times the distance from the spark gap to the 
end of the wire.) 

Make the sending aerial longer by adding the coil of the helix 
between the spark and the wire leading to the aerial. Make the 
receiving aerial short by connecting the receiving instrument to 
its midpoint. Use a simple tuner on the receiving aerial and 
move the slide into the position which gives the best sound in the 
telephone receiver. Set up apparatus to correspond with as many 
of the wiring diagrams as you have time for. If you are in doubt 
about the wiring ask the instructor. 

2. Connect an adjustable condenser or a Leyden jar of proper 
size in parallel with the spark of the induction coil. What effect 
does it have upon the loudness of the spark discharge ? 

3. What effect does the condenser have upon the color of the 
induction coil spark? 

4. What effect upon the operation of the receiving instrument is 
produced by using a condenser (Leyden jars) on the sending 
spark ? 

The sending transformer and the adjustable condenser make it 
possible to vary the wave length of the sending instrument. 

5. What advantage is obtained by changing the sending wave 
length? See Wireless Telegraphy Morgan. 

C. Reference Work. Carhart and Chute. 

6. Make a diagram corresponding to the rapid vibrations of an 
induction-coil spark. See Oscillatory Discharge. 

7. Who discovered electric waves? By what other name are 
they known ? 

8. Who is recognized as the inventor of wireless telegraphy? 
Give date. 

9. What is the audion detector? Diagram it and state what 
it does. 

10. How much time is required for the passage of a wireless 
wave between Paris and Washington ? 



WIRELESS B 

D. General Information. Laws. Amateurs are restricted in 
sending to short wave lengths, and they are limited to compara- 
tively low-power sending apparatus. See Wireless Laws. There 
is no law regarding the receiving of any messages. It is, however, 
illegal to divulge information of a private nature. 

Distance. Buildings, mountains, trees, and especially steel 
structures, interfere with receiving. Wireless waves travel twice 
as far over water as over land, and twice as far after sundown as 
during the day. 

There are a number of stations in America having wave-lengths 
of from twenty-five hundred meters to seven thousand meters. 
It is now possible to send wireless messages completely around 
the globe. 

By using a simple crystal detector receiving set with a sixty-foot 
aerial, including tuner and loading coil, it is possible to pick up 
messages from high power stations more than a thousand miles 
distant. A simple receiving set is commonly used by amateurs to 
get the time from the Arlington government station, which has a 
2500 meter wave length. 

There are over two thousand high-power wireless stations in 
this country capable of transmitting messages over one thousand 
miles distance. Many commercial sending instruments operate 
on wave lengths of from three to six hundred meters. 

APPROXIMATE TRANSMITTING DISTANCES OF SPARK COILS FOR SIMPLE 
SENDING AND RECEIVING INSTRUMENTS 

I inch coil ... 2 miles 2 inch coil .... 16 miles 

\ inch coil ... 3 miles 3 inch coil .... 24 miles 

i inch coil ... 8 miles 4 inch coil .... 32 miles 

i inch coil ... 12 miles 

TABLE OF APPROXIMATE SPARKING DISTANCES 

5,000 volts ... .22 inch 40,000 volts . . . 2.45 inches 

10,000 volts ... .47 inch 50,000 volts . . . 3.55 inches 

20,000 volts . . . i.oo inch 100,000 volts . . . 9.60 inches 

30,000 volts . . . 1.62 inches 150,000 volts . . . 15.00 inches 



2l6 LABORATORY PROJECTS IN PHYSICS 

87. CARBURETOR A 

To study the construction and operation of a carburetor. 

MATERIALS. Bunsen burner; ignition bottle; large glass jar; one or 
more sectional carburetors. 

A. Preliminary Work. The purpose of a carburetor is to mix 
air and gasoline vapor in the proper proportion to obtain effi- 
cient combustion. 

Note that a Bunsen burner has two adjustments ; one for con- 
trolling the gas flow and one for controlling the air flow. The 
purpose of these adjustments is to mix air and gas in proper propor- 
tion before they reach the flame. A Bunsen burner is a carburetor. 

1. Close the air inlet completely, and light the burner. The 
flame is now operating with a " rich mixture," insufficient 
supply of air. Describe the flame under these conditions. 

2. Gradually open the air inlet of the burner until sufficient 
air is admitted to cause the flame to " strike back " to the bottom 
of the burner tube. Do not permit it to burn for more than a mo- 
ment at the bottom. Describe the flame when the air inlet is open. 

3. Fill the ignition bottle with water and invert it in the jar of 
water. Allow illuminating gas from a rubber tube to bubble into 
the bottle, displacing the water. When the bottle is filled with 
gas, remove it and ignite the gas in the bottle with a match. In 
the same way remove the bottle when it is half full of gas, allow- 
ing air to mix with the gas so that you have a mixture of half gas 
and half air. Try one-fourth gas and one-fifth gas. Which burns 
most vigorously or forcefully? 

B. Carburetor Mechanism and Function. Examine a car- 
buretor in section. The common types of carburetors consist of 
two main compartments, the float chamber and the mixing 
chamber. The purpose of the float chamber is to hold a supply 
of gasoline from the tank ready for use in the mixing chamber. 
It must keep this supply at a constant level. The purpose of the 



CARBURETOR A 



217 



mixing chamber is to provide for mixing a fine spray of gasoline 
with the air as it is drawn through the carburetor by the suction 
of the engine. In answering questions refer to Motor Vehicles 
Frazer and Jones Chapter on Elements' of Carburetion. 

mzi n run . 



Thrott/e Va/ve 




F/oat 



Chamber 



_ SprayJVozz/e 



Airfn/et 



FIG. 90. Sectional view of a simple form of carburetor, showing float chamber and 

mixing chamber. 

4. What is the purpose of the float ? 

5. What is the function of the float needle? 

6. Of what material is the float made? 

7. Explain the sequence of operations which cause gasoline 
to enter from the tank into the float chamber. 

8. Explain what causes gasoline to stop flowing from the tank. 

9. What might cause a carburetor to flood (overflow) ? 

10. What is the function of a spray needle? See fig. 91. 

11. If the spray needle is more nearly closed, how is the mix- 
ture affected and vice versa? 



2l8 



LABORATORY PROJECTS IN PHYSICS 



12. Where is the choker or choke valve located, and what is its 
function ? 

13. How is it possible to obtain a richer mixture by means of 
the choker? 

14. What is the function of the throttle? 



A/r/n/et 



ThroU/e Va/ve 
F/o&t J7eeJ/e L e vers 




Spray Nee d/e 

FIG. 91. Carburetor, showing spray needle and auxiliary air inlet. 

15. Why does the mixture tend to become very lean when the 
throttle is nearly shut? 

1 6. For what purpose is wire gauze used at the entrance to the 
float needle valve ? 

17. What is the purpose of the drain-cock at the bottom of the 
carburetor ? 

18. What is a Venturi tube ? 






CARBURETOR B 2IQ 



88. CARBURETOR B 

To study the construction, operation, and adjustments of 
carburetors. 

MATERIALS. A number of different makes of carburetors, if possible, 
some in section. Second-hand carburetors may be used. 

A. Carburetion. When automobiles were first introduced, 
high-grade gasoline (volatile gasoline) was very cheap. Because 
the gasoline vaporized readily, carburetors were made in very 
elementary form surface carburetors. As the demand for fuel 
increased, and with it the necessity of including in the fuel some of 
the heavier distillates, the problem of carburetor design and con- 
struction became more complex. Besides changes in the nature of 
the fuel, the demand arose for carburetors which would provide 
a more efficient mixture for wider variations in engine speed. 

All simple forms of carburetors produce rich mixtures at high 
speed. If the mixing valve is set for high speed, the mixture is 
too lean for low speed. A simple carburetor that will produce a 
well-balanced mixture for all speeds has not yet been devised. 
Properly proportioned mixtures for the different speeds can be 
obtained approximately with complicated carburetors containing 
properly designed and adjusted auxiliary air valves. These car- 
buretors are accordingly more expensive. 

B. Reference Work. Use Motor Vehicles or other text. 

1. What is meant by carburetion? 

2. What determines the efficiency of combustion? 

3. Are surface or spray carburetors more commonly used 
to-day ? 

4. Name four valves common to carburetors. 

5. Diagram a carburetor containing an auxiliary air port. 
Name the parts. 



220 



LABORATORY PROJECTS IN PHYSICS 



Mixture 
to Engine 




I 



CARBURETOR B 221 

C. Troubles and Adjustment. 

6. What is the purpose of a secondary or auxiliary air inlet on 
a carburetor ? 

7.. What is meant by " adjusting a carburetor " ? 

8. If the float should leak, what effect might be produced 
upon the carburetor? 

9. A very lean mixture burns slowly. Explain how this may 
result in an explosion in the carburetor (popping back) when the 
engine runs slowly. 

10. If the ignition current is shut off in going down a hill and 
the engine is allowed to run, a loud explosion sometimes occurs in 
the muffler at the bottom of the hill when the current is again 
turned on. Explain. 

11. How can a " rich mixture " be detected? 

12. What are some causes of a " lean mixture"? 

13. If a piece of dirt should become clogged in the float needle 
socket, what might be the result? 

14. By what change of adjustment could you make the mixture 
richer in case the engine missed fire, or developed insufficient 
power on account of the mixture being too lean? 

15. State some important steps in the adjustment of a carbu- 
retor. See Frazer and Jones. 






222 LABORATORY PROJECTS IN PHYSICS 

89. FORD ENGINE A 
To study the construction and operation of the Ford engine. 

NOTE. This experiment should be preceded by experiments, Gasoline 
Engine A and Gasoline Engine B. 

MATERIALS. Ford chassis, second-hand (radiator, cylinder head, and 
one piston removed); reference books, The Model T Ford Car, Page, and 
The Ford Manual. 

The most expensive and the largest single unit of the auto- 
mobile mechanism is the engine. Upon its design, material, and 
workmanship, the efficiency of the operation depends. An engine 
that is defective in design or adjustment may be very wasteful of 
gasoline. If the parts of the engine include cheap material and 
cheap workmanship, its life may be only half as long as it should 
be. The modern gasoline engine has required years of experi- 
mentation and the combined labors of many expert engineers. 
To appreciate it properly, as a contribution to human comfort 
and to modern commercial life, it is necessary to know its principal 
parts and to learn how each part is related to the general operation. 
The Ford engine has become famous because it is powerful for its 
size, it is efficient in the use of gasoline, and it stands up well 
under hard service. 

A. General Characteristics and Operation. This is an L-type 
motor. (Intake and exhaust valves are on the same side. The 
T-type engine has intake on one side and exhaust on the opposite 
side.) Remove the cylinder head. Take out bolts with a wrench. 
In answering questions refer to Ford Manual and to The Model 
T Ford Car Page. 

1. Are these cylinders cast as a single unit (en bloc), or in 
parts ? 

2. What important part of the ignition system is attached to 
the cylinder head ? 



FORD ENGINE A 



22 3 




224 



LABORATORY PROJECTS IN PHYSICS 






' : \ 




FiafiQ 
lnifc 

5tt*i 

N *M 

ii 





/ .' \ vfc 

\-> --'';\ 1 

^;s;^ | 



FORD ENGINE A 22$ 

3. How many shafts are inclosed- in the crank case? Name 
them. What are their purposes? 

4. How are the intake and exhaust valves operated? 

5. What operates the cam shaft? 

6. How many cams are on the cam shaft ? 

7. How fast does the cam shaft revolve with respect to the 
rate of the crank shaft? 

8. What pushes the valves open? 

9. What closes the valves? 

10. What is the direction of motion of any piston, (a) when its 
intake valve opens, (b) when its exhaust valve opens? 

B. The Crank Shaft. Look into the open cylinder and 
observe the crank shaft. Have some one crank the car and you 
will note that the crank shaft revolves. 

11. At what angle do the cranks stand with respect to each 
other in a four cylinder engine ? 

12. How are the crank bearings and the pistons oiled? 

13. Name four important parts of the mechanism between the 
crank shaft and the rear wheels. 

C. The Pistons. One of the pistons has been removed for 
examination. The connecting rod attaches the piston to the 
crank shaft. 

14. How does a well-oiled piston aid compression? 

15. How many rings has the Ford piston? 

1 6. What is the purpose of piston rings? 

17. What kind of combustible mixture tends to deposit carbon 
on the piston and valves? 

1 8. What causes old pistons to leak and lose compression? 



226 



LABORATORY PROJECTS IN PHYSICS 



Steer /no A. 



front Axfe 



Front Whee/ 



Cofn/7>u(3fo/~ 




/fub Brak 
Assemb/y 



Differentia/ Gear- 



/fear Spring 



FIG. 95. The Ford chassis, showing location of important parts of the mechanism. 



FORD ENGINE B 



227 



90. FORD ENGINE B 

MATERIALS. Same as in Ford Engine A. Reference Book, The Model 
T Ford Car, Page. 



FanAssb. 

tinder ffead 

//nc/er Cast/ng 
Cy//nderfn/et Connect/on. 




Jvt/ef Conn. P/pe ~ - > 
i Fan Jfous/ntp 
^ Lower Jfose 
Lower ffose C/t/> 
Rad. Out/et Conn. 
Drain Cock *"'' 

. Lower Tank 
FIG. 96. The Ford cooling system a convection circuit. 

A. The Ford Timer. Remove the timer cap. The purpose 
of the timer is to determine the time at which current is sent to 
each induction coil and consequently to each spark-plug. 

1. To which shaft is the timer attached? 

2. How many contact points does the timer have? 

3. What touches these points, sending currents to the induc- 
tion coils and spark plugs ? 



228 LABORATORY PROJECTS IN PHYSICS 

4. How many sparks are produced in this four cylinder engine 
for each turn of the crank-shaft ? 

5. Where is the electric generator located in the Ford? 

6. What is the sequence of firing in the cylinders, beginning 
at the front as No. i ? Sequence of opening of intake valves. 

B. The Cooling System. (Thermo- Siphon.) The Ford cylin- 
ders are cooled by convection. Examine the openings between 
the walls of the cylinder for water circulation. 

7. Why is it necessary to have a cooling system? 

8. What would be some of the results if the engine were op- 
erated without water in the cooling system? 

9. In which direction does the water flow? 

10. Explain what causes the water to circulate. 

11. State two possible causes of trouble in the cooling circuit. 

12. What chemicals are used to prevent freezing in winter? 

C. Lubrication. The life of an automobile engine depends 
upon proper lubrication of the working parts. Automobile engine 
pistons move at rates as high as one thousand to fifteen hundred 
feet per minute. The metal of the pistons, piston rings, and the 
cylinder wall will rapidly wear away unless an abundance of proper 
oil is provided. 

13. Explain the operation of a splash system of oiling. 

14. What provision has the Ford for circulating the oil? 

15. In what part of the crank case does the oil stand? 

1 6. If the engine should become overheated, how would this 
affect the engine oil? 

17. What parts of a crank shaft need oil? 

1 8. What parts of a piston connecting rod need oil? 

D. The Manifolds. Note the position of the intake manifold 
which leads the combustible mixture from the carburetor to the 
intake valves. The exhaust manifold leads the burnt gases from 
the exhaust valves to the muffler. 



FORD ENGINE B 



229 




230 



LABORATORY PROJECTS IN PHYSICS 



91. IGNITION SYSTEMS A SIMPLE 
To construct and operate simple ignition systems. 

MATERIALS. Four dry cells ; insulated wires ; vibrating induction coil ; 
metal ring stand; automobile spark plug. (Part of the apparatus for this 
experiment must be obtained from the instructor.) 




nc/uction Coi/ 



Dry Ce//2 
A 



Primary cfrcuif 



Touch this 
to the second 
primary termina/. 




L 



JT 



Secondary circuit 



W/re grounded 

to meta/of the 

automoMe. 



Dry Ce//s 



Make touch 
con/act here 



Induction 
Coi/ 




FIG. 98. Simple ignition system containing primary and secondary circuits. 

A. The Induction Coil. An ignition system in a gas engine, 
or an automobile, is used to produce a hot spark for igniting the 
explosive mixture in the engine cylinder. This may be accom- 
plished by sending a six-volt current through an induction coil, 
and thereby increasing the voltage to ten or fifteen thousand 
volts. This high voltage current will pass through air for a short 
distance, producing a very hot spark. 

Operate a vibrating induction coil as follows: Attach a short 
wire from one of the secondary terminals of the induction coil to 



IGNITION SYSTEMS A SIMPLE 



231 



within a quarter of an inch of the other secondary terminal, but 
not touching it. This quarter-inch opening will form the spark 
gap. An induction coil should not be operated with the spark 
gap too wide, as this may puncture the insulation of the secondary 
coil and ruin it. Connect four dry cells in series. (Caution. The 
current from the secondary terminals of an induction-coil is dangerous. 
Keep away from it.} Attach one wire from the dry cells to one of 
the primary terminals of the induction-coil. Touch the other 
wire from the dry cells to the other primary terminal of the induc- 
tion coil. A spark should jump across the spark gap of the second- 
ary terminals. Do not handle the induction coil without first 
disconnecting the dry cells. 

1. Diagram an induction coil. See Carhart and Chute or 
Millikan, Gale and Pyle. 

2. Should the current which passes through the primary 
winding of this type of coil be a continuous flow, or an intermit- 
tent flow? 

3. Explain the purpose of the vibrator. If the vibrator does 
not operate, it may need some adjustment. Consult the instructor. 

4. What pulls the vibrator toward the coil? What draws it 
back? 

5. What is a condenser made of? What is its function? In 
automobile ignition systems, the timer usually serves the purpose 
of the vibrator and the induction coil does not contain a vibrator. 

B. The Secondary Circuit Spark Plug. Disconnect the bat- 
teries, temporarily, from the induction coil. Remove the wire 
from the secondary terminals. Fasten an automobile spark plug 
to the clamp of the ring stand. Connect a well-insulated wire from 
one secondary terminal of the induction coil to the spark plug. 
Connect a second wire from the other secondary terminal to any 
metal part of the ring stand. Operate the induction coil as before 
and the secondary current should jump across the spark gap of 
the spark plug. 



232 LABORATORY PROJECTS IN PHYSICS 

6. Diagram a sectional view of a spark plug and tell of what 
materials it is made. See Motor Vehicles Frazer and Jones. 

7. The secondary circuit is grounded through the ring stand. 
What is meant by the term " grounded circuit "? 

C. Reference Work. Automobiles Zerbe. 

8. What is meant by the expressions " high-tension current," 
and " low- tension current"? 

9. What should be the width of the spark gap on a spark- 
plug? 

10. What three common methods are employed for producing 
current for ignition purposes? 

11. What are the two common types of magnetos? 

12. How can the sparkplug of an automobile be tested to 
insure that it sparks ? 

13. State three possible causes of trouble in the electric cir- 
cuits. 

92. IGNITION SYSTEMS B 

To study the operation of automobile and gas engine ignition 

systems. 

MATERIALS. Four dry cells ; vibrating induction coil ; four metal ring 
stands ; four spark plugs ; wooden block with four binding posts ; non- vibrating 
induction coil (make and break coil) . (Part of the apparatus for this experiment 
must be obtained from the instructor.) 

A. Automobile Ignition System. Attach four spark plugs to 
four ring stands. Connect the four stands by means of a wire, 
and extend this wire to one terminal of the induction coil. From 
the four spark plugs lead four well-insulated wires to four binding- 
posts placed near the corners of a square, wooden block. Attach 
a well-insulated wire to the second terminal of the vibrating 
induction coil. Insulate this wire by pulling a piece of rubber 
tubing over it. (Caution. The secondary current is dangerous. 



IGNITION SYSTEMS B 



233 



Keep away from the secondary wires when the batteries are attached.) 
When this wire is placed in contact with any one of the posts on 
the wooden block, you should get a spark at the spark plug which 
that post controls This block with the four posts represents the 
u distributor " of a four-cylinder automobile ignition system. 




yncfuction Co// 

T/'mer - snake 
, touch contacfhere. 

FIG. 99. Ignition system, illustrating the operation of the timer and the distributor 

on an automobile. 

The closing of the battery circuit (primary circuit) by touching 
one wire to one of the primary terminals of the induction coil, 
represents the " timer " of an automobile ignition system. 

Automobiles as a rule do not have vibrating coils. The timer 
makes and breaks the primary current, serving the purposes of the 
vibrator. The Ford ignition system is an exception. The Ford 
car is provided with four vibrating coils, one for each cylinder. 

In many of the common types of cars, the low voltage current 
supply for operating the induction coil is taken from the storage 
battery. 

i. Diagram the apparatus used above, showing dry cells, induc- 
tion coil, spark plugs, and distributor. 



234 LABORATORY PROJECTS IN PHYSICS 

2. State one sequence of firing for a four-cylinder engine. See 
Page. 

3. What is the purpose of the ignition switch on the instrument 
board of an automobile ? 

4. What is the purpose of the distributor? 

B. Make-and-break Ignition. Some gas engines are operated 
by a " make-and-break " spark (wipe spark). Connect up four 
dry cells. Connect a wire from one terminal of the battery to a 
simple make-and-break coil. This device consists of a coil of wire 
wound around an iron core. Slip a heavy rubber tube over the 
second wire from the battery, for insulation. Touch the second 
terminal of the make-and-break coil with the second wire from 
the battery, and pull it quickly away. Use one hand only to avoid 
a shock. A hot spark will occur at the time of break, due to the 
self-induced current in the coil. If this make-and-break occurs 
in the cylinder of an engine, the spark may be used for ignition. 

5. Diagram a make-and-break ignition system. See The 
Gasoline Automobile Hobbs, Elliott, and Consoliver. 

C. Magneto Generators. Magnetos are sometimes employed 
as sources of current for ignition. These generators take the place 
of the battery. They are either of the high-tension or the low- 
tension types. The low-tension magneto requires a separate in- 
duction-coil. The high-tension magneto contains the induction 
coil in the magneto. 

D. Reference Work. The Gasoline Automobile Hobbs, Elli- 
ott, and Consoliver. 

6. Make a diagram showing the main parts of a typical ignition- 
system, including induction coil and distributor. 

7. State at least five possible causes of failure of an ignition 
system to produce a spark. 



IGNITION SYSTEMS C, FORD IGNITION 235 

93. IGNITION SYSTEMS C, FORD IGNITION 
To study and operate the Ford ignition system. 

Reference. The Model T Ford Car Page. 
MATERIALS. Ford engine. Five dry cells. 

A. The Sequence of Firing. If you examine the positions of 
the pistons of the engine, you will note that when No. i and No. 4 
are on top center (all the way Up), No. 2 and No. 3 are on the 
bottom center (the lowest point they reach in the cylinder), and 
vice versa. This is the case with all typical four-cylinder, four- 
cycle, gasoline engines. The cranks, therefore, are set one-half 
a revolution or 180 apart. 

In a four-cycle, four-cylinder engine, the complete operation 
consists of four strokes, or half revolutions intake, compression, 
explosion, and exhaust. The explosion occurs on or near the top 
center of the compression stroke in each cylinder, the other top 
center being the top center of the exhaust stroke. However, the 
valves and cranks are so set that at every half revolution one of 
the cylinders is ready to fire. Suppose that No. i and No. 4 are 
on top dead center. One is on top center of the compression 
stroke, and the other is on top center of the exhaust stroke. 

A four-cylinder engine may fire in the sequence one, three, four, 
two, or one, two, four, three. 

1. Locate the four intake valves by their connection with the 
intake manifold. Number them in the series of eight valves, be- 
ginning at the front. 

2. Determine the firing sequence of the cylinders by noting the 
sequence of the opening of the intake valves. The firing sequence 
is the same as the valves sequence. 

B. The Induction Coil. An induction coil is a device for in- 
creasing the voltage of a few dry cells in order to obtain a hot 
spark. Four dry cells deliver about six volts. At this pressure 



236 LABORATORY PROJECTS IN PHYSICS 

(voltage) the spark is insignificant and could not be used for 
ignition. However, if this current is sent through an induction- 
coil, the pressure from the secondary terminals of the coil is changed 
to ten or fifteen thousand volts. This high-voltage current will 
easily jump across the terminals of a spark plug and make a hot 
spark. (Caution. The high-voltage current from the secondary of 
an induction-coil is very disagreeable and sometimes dangerous. Be 
careful. Do not attach the batteries to the primary terminals until 
all other connections are made. Keep hands away from the secondary 
circuit when the primary is operating.) Connect one of the second- 
ary terminals of a separate induction coil (use one of the laboratory 
coils) to one of the spark plugs in the cylinder head by means of 
an insulated wire. Connect the other terminal to the frame of the 
car. Attach four dry cells to the primary terminals of the coil in 
series with a telegraph key as a make-and-break. Operate the 
spark across the spark plug by pushing the key. 

3. How does the secondary current flow from the one terminal 
attached to the spark plug back to the other terminal of the coil ? 

C. The Wiring, Timer, Coils, Spark Plugs. The charge is 
exploded in each cylinder by an electric spark which jumps across 
the points of the spark plug. Each spark plug receives its current 
from the induction coil to which it is attached. The Ford has a 
separate vibrating coil for each spark-plug. The time at which 
the spark occurs is regulated by the timer which is inclosed in the 
round, aluminum casting with four terminals situated to the left 
of the crank-handle of the engine. It is held in place by a steel 
clamp. Push the clamp aside, take off the timer cap and examine 
it. Now crank the engine over and see what happens to the little 
roller which the cap covers. Refer to The Model T Ford Car or 
The Ford Manual. 

4. What is the function of this roller ? 

5. At what rate does the timer revolve with respect to the 
speed of the engine? 



IGNITION SYSTEMS C, FORD IGNITION 



237 



6. To the end of what shaft is the timer attached? 

7. What causes this shaft to revolve ? 

8. What other office does this shaft perform ? 

9. The timer cap is attached to the spark lever on the steering 
wheel by means of a rod. How does moving the spark lever ad- 
vance or retard the time of the spark in the cylinders? 




Co/7 C/n/ts 
FIG. 100. The Ford ignition system. 

10. When the engine is running fast, should the spark be ad- 
vanced or retarded to get best power ? 

1 1 . With respect to the explosion in the cylinder, what is meant 
by advancing or retarding the spark? See Zerbe, Page, or Hobbs, 
Elliott, and Consoliver. 

Replace the timer cap, reset the clamp and connect four well- 
insulated wires from the four terminals of the timer cap, to the 
four upper terminals of the coil box. At the timer cap these 
wires should touch only the binding posts, not the cap or engine 
metal. Connect the four lower terminals on the coil box with 
the spark plugs by means of well-insulated wires. Make a dry 
cell battery by connecting five or six cells in series, and connect 
one terminal of the battery to the lower left-hand terminal on 
the coil box. Ground the other terminal of the battery by con- 
necting a wire from it to some metal part of the engine. Now 



LABORATORY PROJECTS IN PHYSICS 




s-lss S' 

^ s 

S s 



IGNITION SYSTEMS C, FORD IGNITION 239 

push the switch on the front of the coil box over to the left, and 
crank over the engine. Notice the sequence of firing and if it is 
not the proper sequence as determined in A , change the wires lead- 
ing from the timer to the coil, or from the coil to the spark plugs, 
until the sequence is correct. 

12. Remove one of the wires leading to the terminals of the 
timer cap. Touch the engine metal with it. Explain the result. 
What is a grounded circuit ? 

13. If the ignition switch on the coil box is set to take current 
from the dry cells, and the car stops with timer roller in contact 
with one of the wires leading to an induction coil, what would be 
the effect upon the dry cells ? How can the driver prevent this ? 

D. The Ford Generator. The Ford should be started on the 
dry cells. When the engine is running, the switch on the coil box 
can be turned, connecting the coils with the generator in place of 
the dry cells and thus save the dry cell current. 

The Ford generator is a special type of low tension, magneto 
generator attached to the flywheel. A number of large bar mag- 
nets are attached to the flywheel. These magnets move in the 
presence of a series of coils of wire attached to a stationary frame. 
These magnets induce an alternating current in the coils. This 
current is used for operating the induction coils. 

14. Attach a wire from the top of the coil frame on the gen- 
erator to the lower right-hand post on the coil box. Turn the coil 
switch, connecting up the magneto. If the engine is now cranked 
rapidly, the magneto will operate the induction coils and spark 
plugs. 



240 



LABORATORY PROJECTS IN PHYSICS 



94. STORAGE BATTERY A 

To study the construction and operation of a lead storage 

cell. 

MATERIALS. Simple storage cell; dilute solution of common salt; 
battery voltmeter ; ammeter ; electric bell ; 2- volt lamp ; small 2-volt motor ; 
lamp board and one-ampere lamp ; i lo-volt or lower voltage direct current. 

Caution. Sulfuric acid will destroy clothing and came burns. Handle with ex- 
treme care. 

Guttet for //O vo/t direct current 

/ 

D 




Positive 
p/ate 



Negative 
p/ate 



4 




Jar with /ead p/ates 
one/ su/fur/c acid. 



One Ampere /amp 
resistance. 




FIG. 102. Wiring scheme for charging a simple storage battery. 

A. Make a simple storage cell by filling a battery jar three- 
fourths full of a twenty per cent solution of sulfuric acid. Sus- 
pend in it two plates of ordinary sheet lead, by folding the lead 
plates over the edges of the jar. With a one-ampere lamp as 
rheostat, prepare to send a no- volt direct current through the 
cell, or to send a direct current from a small generator. (Caution. 



STORAGE BATTERY A 



241 



Do not connect the cell directly to the line-wires without resistance, as 
this would blow out the fuse.) Test the charging current with a 
salt solution (a quarter teaspoonful in a tumblerful of water) to 



Outtet for //O vo/t direct current 




One Ampere. 
res/stance . 



Wafer 
a few grra/ns of 
common sa/t-- 
<Socfium Ch/or/de. 



FIG. 103. Wiring for testing a direct current for positive and negative terminals. 

find which terminal is negative. In making this test attach the 
lamp in series with one wire to insure against a short circuit if the 
wires should accidentally touch in the salt solution. The negative 
terminal gives off more bubbles. Connect the brown-coated plate 
(positive) to the positive terminal of the line current. In charging, 
connect positive to positive and negative to negative. 

The charging current should pass through the cell from positive 
to negative. Hydrogen is set free at the negative plate and 
oxygen at the positive (electrolysis). The oxygen, instead of 
escaping into the air, attacks the lead, forming a brown coat of 
PbO 2 , lead peroxide. When the cell is charged, the positive plate 
coated with lead peroxide and the negative plate of pure lead act 
similar to the positive and negative plates of any simple liquid cell. 

Allow the current to pass through this cell for fifteen minutes. 



242 LABORATORY PROJECTS IN PHYSICS 

(Read Black and Davis on the storage battery.) Disconnect 
from the charging lines and test the pressure with a voltmeter. 
(Caution. Do not connect an ammeter to a storage battery without 
some resistance as a motor or a lamp in series with the meter , as this 
might ruin both the ammeter and the battery.) 

1. What is the voltage of a lead storage cell? See texts. 

2. Ring an electric bell. Measure the amperage which the bell 
takes. 

3. Operate a small motor and measure the amperage. 

4. What happens to a storage battery if the wires are connected 
without resistance (some suitable lamp or motor)? 

B. Chemical Reaction. Disregarding intermediate steps in the 
chemical reaction, we may represent the operation as follows : 

Charged condition Discharged condition 

Pos. Elec- Neg. Pos. Elec- Neg. 

Plate trolyte Plate Plate trolyte Plate 

PbO 2 + 2H 2 SO 4 + Pb Z: PbSO 4 + 2H 2 + PbSO 4 

The reaction goes in the opposite direction when a current is 
reversed through the cell in the operation of charging it. The cell 
does not store up electricity. The energy of the charging current 
is used in the formation of lead peroxide on the positive plate. 
When the charging current stops, the two plates, on account of 
their different chemical nature, act like a simple liquid cell, which, 
on account of the chemical difference between the two plates, is 
capable of producing a reaction with the electrolyte and generating 
a current. The hydrogen ions of the sulfuric acid unite with the 
oxygen of the lead peroxide, forming water, and SO 4 ions go to 
produce lead sulfate on both plates. Thus on full charge the sul- 
furic acid is concentrated and on discharge it is dilute. The spe- 
cific gravity is, therefore, a fairly good test of the charged or dis- 
charged condition of the cell. The electrolyte, however, must be 
kept full by the addition of distilled water, since evaporation 
reduces it. 



STORAGE BATTERY B 243 

Reference Work. Black and Davis, Practical Physics. 

5. When a storage battery is discharged what chemical com- 
pound covers the plates? 

6. What are some disadvantages of a lead storage battery? 

7. What efficiency is obtained from a battery in good condition ? 

8. Mention three uses for storage batteries. 

9. In the Edison storage battery what are the plates composed 
of and what electrolyte is used? 

95. STORAGE BATTERY B 

MATERIALS. Storage Battery (commercial type preferably in glass 
jar) ; battery hydrometer ; battery ammeter, rheostat. 

Caution. Sulfuric acid will destroy clothing and cause burns. Handle with 
extreme care. 

A. Operation and Care. Examine the large storage batteries. 
Test by means of a salt solution as in Storage Battery A to 
find which terminal is negative. Test the line current also to 
find which terminal is negative. With a three-ampere rheostat 
in series, prepare to force a current through the battery in reverse 
direction (positive connected to positive, and negative to nega- 
tive). (Caution. Have your scheme of wiring inspected by an 
instructor before turning on the current, to avoid a possibility of 
ruining the batteries.} If necessary, distilled water should be added 
so that the electrolyte stands one quarter inch above the plates. 
The time required for complete charge from condition of discharge 
is usually fifteen to twenty hours. 

1. Do not attach an ammeter without resistance. Why? 

2. Note the specific gravity at the beginning of charge. 

3. Charge for fifteen minutes. This brief time will not make a 
noticable change on the specific gravity. Does the acid become 
more or less concentrated on charging? Refer to texts. See 
Black and Davis. 

4. What is the combined voltage of two cells in series ? 



244 



LABORATORY PROJECTS IN PHYSICS 



5. Attach a suitable motor in Series with a battery ammeter and 
operate it. How much current does the motor take ? 

Storage batteries are commonly rated as having a certain output 
in ampere-hours. An ampere-hour means a flow of one ampere 
for one hour. A twenty-ampere-hour battery means that the 




FIG. 104. A storage battery operating a motor with an ammeter in the circuit. 

battery can supply a current of one ampere for twenty hours, 
after which it should be recharged. If larger amperages are 
taken, the time will be reduced. 

B. Care of Lead Battery, (a) Use only pure water and pure 
acid for electrolyte. (&) Avoid overcharging and overdischarging. 
(c) Do not allow the battery to stand discharged, as it will become 
sulfated and sometimes permanently injured. 

In the self-starting systems of automobiles, storage batteries 
are required to deliver fifty to two hundred amperes at about six 
volts for a few moments in starting the engine. This large amper- 
age would soon exhaust a storage battery. The starting motor 
should be operated for very short periods only. Lead storage 
batteries are well suited for this work, because they can deliver 



STORAGE BATTERY B 245 

an enormous current for a short time, due to their very low internal 
resistance. Automobile storage batteries have a specific gravity 
at complete charge 1.3, and at complete discharge 1.15. 

C. Reference Work. Electricity Experimentally and Practically 
Applied Ashe. 

6. When was the storage battery invented and by whom? 

7. What two forms of lead are used in the making of plates? 

8. How does the formation of lead sulfate reduce the efficiency 
of the cell? 

9. What is meant by the expression, lo-ampere, eight- 
hour cell? 

10. If cells are discharged too rapidly, what tends to reduce 
their efficiency ? 



APPENDIX 

LABORATORY REFERENCE SHELF 

A. PHYSICS TEXTS. 

Practical Physics Black and Davis 3 copies 

The Macmillan Co., N. Y. 
Practical Physics Millikan, Gale and Pyle 3 copies 

Ginn & Co., N. Y. 
Physics With Applications Carhart and Chute 3 copies 

Allyn & Bacon, Boston. 
Physics Mann and Twiss 3 copies 

Scott Forsman & Co., Chicaro. 
Essentials of Physics Hoadley 3 copies 

American Book Co., N. Y. 
The Ontario Physics Merchant and Chant 3 copies 

The Copp, Clark Co., Ltd., Toronto, Canada. 
Household Physics Butler 2 Copies 

Whitcomb & Barrows, Boston. 
Household Physics Lynde 2 copies 

The Macmillan Co., N. Y. 
College Physics Kimball i copy 

Henry Holt & Co., N.Y. 

B. GENERAL SCIENCE TEXTS. 

General Science Barber - 2 copies 

Henry Holt & Co., N. Y. 
General Science Hodgdon . . v 2 copies 

Hyndes, Hayden & Eldredge, N. Y. 

C. BOOKS ON SPECIAL SUBJECTS. 

Mechanics of the Household Keene 2 copies 

McGraw-Hill Book Co., N. Y. 
The Wonder-book of Light Houston i copy 

Frederick A. Stokes & Co., N. Y. 
How to Make Good Pictures i copy 

Eastman Kodak Co., Rochester. 
Electricity Experimentally and Practically Applied Ashe . . i copy 

D. Van Nostrand Co., N. Y. 
247 



248 LABORATORY PROJECTS IN PHYSICS 

Elements of Electricity Timbie i copy 

John Wiley & Sons, N. Y. 
Weather Jameson i copy 

Taylor Instrument Companies, Rochester. 
Mechanics of the Sewing Machine N. E. A. Bulletin ... 5 copies 

Singer Sewing Machine Co., N. Y. 
Smithsonian Physical Tables i copy 

Smithsonian Institution, Washington, D. C. 
Motor Vehicles Frazer and Jones i copy 

D. Van Nostrand Co., N. Y. 
The Gasoline Automobile Hobbs, Elliott and Consoliver . . i copy 

McGraw-Hill Book Company, N. Y. 
The Model T Ford Car Page i copy 

Norman W. Henley Pub. Co., N. Y. 
Wireless Telegraphy and Telephony Morgan i copy 

Norman W. Henley Pub. Co., N. Y. 

BOOKS FOR REFERENCE AND READING 

NOTE. A briefer list includes those marked with a star. 

GENERAL READING 

* The Wonders of Science in Modern Life (10 small volumes) Williams 

Funk & Wagnalls Co., N. Y. 
Romance Series Historical, Informational, Interesting. Volumes on : 

* Aeronautics. Engineering. 

* Submarine Engineering. Locomotion. 
Modern Electricity. Mining. 
Astronomy. * Photography. 

Seeley Service & Co., London, also 
J. B. Lippincott & Co., Philadelphia. 

* Inventors at Work lies. 

Doubleday, Page & Co., N. Y. 

* Leading American Inventors lies. 

Doubleday, Page & Co., N. Y. 
Stories of Useful Inventions Forman. 
Century Co., N. Y. 

* A Century of Electricity Mendenhall. 

Houghton, Mifflin & Co., Boston. 
All About Inventions and Discoveries Talbot. 
Funk and Wagnalls Co., N. Y. 



APPENDIX 249 

Boys' Book of Inventions Baker. 

Doubleday, Page & Co., N. Y. 

* The Boys' Life of Edison Meadowcrof t. 

Harper & Bros., N. Y. 
Galileo His Life and Work Fahie. 

James Pott & Co., N. Y. 
Heroes of Science Physicists (out of print). 

E. and J. B. Young & Co., N. Y. 
Famous Men of Science Boulton. 

Thomas Y. Crowell & Co., N. Y. 
Children's Stories of the Great Scientists Wright. 

Chas. Scribner's, N. Y. 

GENERAL BOOKS OF REFERENCE 

* Ganofs Physics Atkinson. 

Wm. Wood & Co., N. Y. 
A Text Book of Physics Watson. 

Longmans, Green & Co., N. Y. 
General Physics Crew. 

The Macmillan Co., N. Y. 

* Architects and Builders Pocket Book. 

John Wiley & Sons, N. Y. 

Bulletins of U. S. Bureau of Standards and Department of Agriculture. 
Washington, D. C. 

* Smithsonian Physical Tables. 

Smithsonian Institution, Washington, D. C. 
Physics of Agriculture King. 

Mrs. F. W. King, Madison, Wis. 

* Agricultural Engineering Davidson. 

Webb Pub. Co., St. Paul, Minn. 

SPECIAL DIVISIONS OF PHYSICS 
A. Mechanics and Heat. 

* A New Astronomy Todd. 

American Book Co., N. Y. 
Astronomy Series Ball. 

J. B. Lippincott & Co., Phila. 

* Astronomy for All Burgel. 

Cassell & Co., London. 



250 LABORATORY PROJECTS IN PHYSICS 

Mechanical Movements, Powers and Devices Hiscox. 
Norman W. Henley Pub. Co., N. Y. 

* All About Engineering Knox. 

Funk & Wagnalls Co., N. Y. 

The Earth's Atmosphere Phixson. 

Chas. Griffin & Co., London. 

* Sounding the Ocean of Air. 

E. S. Gorham, N. Y. 
All About Air Craft Simmonds. 

Funk & Wagnalls Co., N. Y. 
Kite Craft and Kite Movements. 

The Manual Arts Press, Peoria, 111. 

* All About Engines Cressy. 

Funk & Wagnalls, N. Y. 

Practical Steam and Hot Water Heating and Ventilation King. 
Norman W. Henley Pub. Co., N. Y. 

* Home Water Works Lynde. 

The Macmillan Co., N. Y. 

* Heat Ogden. 

Popular Mechanics Co., Chicago. 

* Liquid Air Sloane. 

Norman W. Henley Pub. Co., N. Y. 
Heat a Mode of Motion (Old Classic) Tyndall. 

D. Appleton & Co., N. Y. 
Story of a Tinder Box Tidy. 

E. S. Gorham, Pub. N. Y. 
Motor Vehicles Frazer and Jones. 

D. Van Nostrand Co., N. Y. 

Mechanical Refrigeration, Elevators, and Steam Turbines. 
Joseph G. Branch Co., Chicago. 

B. Light and Sound. 

Waves and Ripples in Water, Air, and Eiher Fleming. 
Edwin S. Gorham, Pub. N. Y. 

* Light Visible and Invisible Thompson. 

The Macmillan Co., N. Y. 

* Moving Pictures Talbot. 

William Heineman, London. 

* The Wonder Book of Light Houston. 

Frederick A. Stokes Co., N. Y. 



APPENDIX 251 



Light-ships and Light-houses Talbot. 

William Heineman, London. 
Color and Its Applications Luckiesh. 

D. Van Nostrand Co., N. Y. 

* Modern Illumination Horstmann and Tousley. 

Frederick J. Drake Co., Chicago. 

* How to Make Good Pictures. 

Eastman Kodak Co., Rochester, N. Y. 

* Photography of Today Jones. 

Seeley Service & Co., London. 

* Theory of Sound in Relation to Music Blaserna. 

D. Appleton & Co., N. Y. 
Sound and Music- Zahm (out of print). 

A. C. McClurg Co., Chicago. 
Sound in its Relation to Music Hamilton. 

Chas. H. Ditson & Co., N. Y. 
The Hand Craft Series Hasluck. 
Violins. 
Pianos, etc. 
David McKay, Pub., Phila. 



C. Electricity. 



* Harper's Electricity Book for Boys Adams. 

Harper & Bros., N. Y. 

* The Boy Electrician Morgan. 

Lothrop, Lee & Shepard, Boston. 

* Harper's How to Understand Electrical Work Onken. 

Harper & Bros., N. Y. 

* All About Electricity Knox. 

Funk & Wagnalls Co., N. Y. 

* Electricity and its Everyday Uses Woodhull. 

Doubleday, Page & Co., N. Y. 
The Elements of Electricity Timbie. 
John Wiley & Sons, N. Y. 

* Alternating Currents Simplified Burns. 

Joseph G. Branch Co., Chicago. 
Electricity Experimentally 6* Practically Applied Ashe. 

D. Van Nostrand Co., N. Y. 
Electricity at High Pressures and Frequencies Transtrom, 

Joseph G. Branch Co., Chicago. 



252 LABORATORY PROJECTS IN PHYSICS 

Essentials of Electricity Timbie. 
John Wiley & Sons, N. Y. 

* Electricity for the Farm Anderson. 

The Macmillan Co., N. Y. 
Wireless Telegraphy 6 Telephony Morgan. 

Norman W. Henley Pub. Co., N. Y. 
Electric Cooking, Heating and Cleaning Lancaster. 

D. Van Nostrand Co., N. Y. 
Matter and Electricity Comstock & Troland. 
(Electron theory in simple language.) 

D. Van Nostrand Co., N. Y. 
Electric Wiring Branch. 

Joseph G. Branch Co., Chicago. - 

D. Books on Special Subjects. 

Hand Craft Series Hasluck (50^ each). 

Electric Bells. Sewing Machines. 

Photography. Telescope Making. 

Electroplating. Microscopes. 

Violins, etc. Dynamos and Motors. 

Photographic Chemistry. Photographic Cameras, etc. 

Pianos, etc. 

David McKay, Publisher, Philadelphia. 
Weather and Weather Instruments Jameson. 
Taylor Instrument Companies, Rochester, N. Y. 

* Flame, Electricity and the Camera lies. 

Doubleday, Page & Co., N. Y. 
Aeroplanes and Dirigibles of War Talbot. 

J. B. Lippincott Co., Philadelphia. 
All About Railways Hartnell. 

Funk & Wagnalls, N. Y. 

* The Modern Clock Goodrich. 

Hazlitt & Walker, Chicago. 
Time Telling through the Ages Brearley. 

Doubleday, Page & Co., N. Y. 
All About Ships Darling. 

Funk & Wagnalls. 

* Submarines Talbot. 

William Heineman, London. 
Laboratory Arts Wollatt. 

Longmans, Green & Co., N. Y. 



APPENDIX 253 

The Panama Canal Haskins. 

Doubleday, Page & Co. 
The Catskill Water Supply of New York White. 

John Wiley & Co., N. Y. 
Physics of Agriculture King. 

Mrs. F. W. King, Madison, Wis. 

* Agricultural Engineering Davidson. 

Webb Pub. Co., St. Paul, Minn. 

* Practical Talks on Farm Engineering Clarkson. 

Doubleday, Page & Co., N. Y. 
The Autobiography of an Electron Gibson. 
J. B. Lippincott & Co., Philadelphia. 

APPARATUS LIST 

NOTE. The prices assigned to the items in this list cannot be relied upon hi 
ordering material. Current prices for material should be obtained from dealers 
before orders are sent. Dealers other than those listed below should guarantee 
to the customer that the material which they supply is strictly in accordance 
with the specifications and quality of material referred to in the list. Success 
in the use of these experiments will depend upon strict adherence to this rule. 
One complete set of apparatus for all experiments in Group I should cost between 
fifty and seventy-five dollars. Abbreviations used below are : 

EA = Eimer & Amend, 205 Third Ave., N. Y. 

SS = Standard Scientific Co., 147 Waverly Place, N. Y. 

WT=Whitall Tatum Co., 46 Barclay St., N. Y. 

LK = L. E. Knott Apparatus Co., Boston, Mass. 

CS = Central Scientific Co., Chicago, 111. 

SR = Sears, Roebuck & Co., Chicago, HI. 

CW = Charles Williams Stores, New York City. 

SP = Stanley & Patterson, 23 Murray St., N. Y. 

GROUP I EXPERIMENTS 

A. Material Used in More Than One Experiment. 

Ai Bells, electric; SS or CW or SP. 631 Acme, size of gong 2^ in. . .60 
A2 Bottles 12 oz. heavy glass ij in. mouth; EA 910-12 oz. . . .10 

A3 Bunsen burner, TerrilFs ; EA 1462 i.oo 

A4 Candles; SS or SR, per doz. 2o?f, Christmas 10 

AS Carbon rods, obtained from worn out dry cells 

A6 Carpet tacks, per box 10 



254 LABORATORY PROJECTS IN PHYSICS 

Ay Cotter-pins, brass, for holding stopper in place on brass piston 
rod, size \ in. diameter X \ in. long ; W. & J. Tiebout, 

1 18 Chambers St., N. Y., $6 per 100 02 

A8 Dry cells, purchase from any electrical store. Red Seal or 

Columbia are reliable 35 

Ag Electric Lamp Pendant Sockets, Miniature (2) ; SS or SR or 

SP, Bryan-t Socket 322 36 

Aio Electric Lamps, Mazda Miniature base, 3 volts (2) at 20^; 

SS or SR or SP 40 

An Funnels; EA 3214, diam. 25 in., short stem 10 

Ai 2 Glass beakers with lip, size 8 oz.; SS 721, at 20^ 40 

Ai3 Glass flasks (2) flat bottom, capacity 500 c.c., heavy glass, 
width of mouth i in. ; in doz. lots, Macbeth Evans Glass 

Co., Pittsburgh, Pa., 1872, or WT, 2016 at 20^ 40 

Ai4 Glass L-tubes, 3-in. arms. These tubes can be made by bend- 
ing 6-in. tubes in a fish-tail Bunsen flame. 4 L-tubes at 

8ff; SS 32 

Ai5 Glass L-tube, one arm 8-in. long, one arm 3-in.; SS . . . . .10 
Ai6 Brass T-tubes, outside diameter ^ in., 2-in. arms, 4 T-tubes; 

EA 7100, \ in. at 38^ 1.42 

Ai7 Glass nozzle-tube (draw 6-in. tube in flame) .06 

Ai8 Glass pressure tube, length 24 in., outside diam. 18-20 mm., 

wall 2-2 1 mm. closed at one end; SS . . 40 

AIQ Glass tubing, outside diam. 7 mm. thickness of wall 151^ mm. 
at 50^ per lb., per ft. 3^; Aioa to Aigcl SS or CS or LK. 

Aiga 2 pieces 24 in. long at .06 12 

Aigb 2 pieces 12 in. long at .03 06 

AIQC 4 pieces 6 in. long at .01^ .06 

Aipd 3 pieces 4 in. long at .01 03 

A2O Hydrometer jar, heavy glass with pour out; WT 2700, height 

12 in., diam., outside, i\ in 60 

A2 1 Laboratory balance; SS, B6oo or CS or LK 6.00 

A22 Lamp Chimney, Macbeth Students Chimney #50; SS, or in 
lot of half gross at $ 6.00, Macbeth Evans Glass Co., Pitts- 
burgh, Pa 15 

A23 Leather sheeting for pump valves (purchase scrap shoe uppers 

from any shoemaker). 
A24 Manometer tube, U-tube, i2-in. arms, outside diam. 10 mm., 

thickness of wall 2 mm. ; SS 2.50 

A25 Half meter stick for manometer tube, inches and millimeters ; 

SS, B7o 3 



APPENDIX 255 

Aa6 Meter sticks, inches on one side and millimeters on other ; 

EA 4298 or SS or LK or CS 50 

Aay Metric weights, i g. to 500 g. ; SS, 6840 3.00 

A28 Nitric acid, technical grade; EA or SS or any chemical dealer .10 
A2Q Piston rods, solid brass, for pumps and hydraulic elevator, 
diam.. \ in., length 12 in., with three in. holes, two at one 

end 1 1 in. apart and one at other end ; SS, 0330 25 

A3o Pocket Ammeter, Eveready Type, 0-35 amp. ; SS or SR or CW .80 
A3 1 Pocket Ammeters and Voltmeters mounted in wood stand 
with binding posts at $2.50; SS. These ammeters may be 
used on i lo-volt alternating current for approximate amper- 
age. On alternating currents the meter registers 75%. 

To correct the reading divide by .75 2.50 

A3ia Ammeter Eveready dashboard type, mounted, o-center, 

o to 15 amperes; SS 5.00 

A32 Pocket voltmeter, Eveready Type o-io volt; SS or SR or CW i.oo 

A33 Push-button, oak ; SS, N62O 10 

A34 Reading glass lens, 2^-in. diameter ; SS K?2oo or SR . . . . 1.15 
A3 5 Ring stands, tripod type, height 36 in., rod diam. f in. ; EA 

6542 at 75^ (2) 1.50 

A36 Ring stand clamps, Bunsen's (without fastener) ; EA 2016, 

small, at 50^ (4) 2.00 

A3 7 Ring stand clamp fastener; E A 2042 at 20^ (4) 80 

A38 Ring stand ring, 2 in. diam. ; EA 6010, diam. 2 in. at 10^ (2) . .20 
A3Q Ring stand ring, 3 in. diam. ; EA 6010, diam. 3 in. at i2ff (3) . .36 
A40 Rubber stoppers, $1.80 per Ib. ; EA or SS or CS. 

# o one hole with hole T \ in diam .02 

# i one hole with hole ^ in diam .04 

A4oc # 2 one hole with hole T s ff in diam 04 

A4od # 5 one hole with hole T 3 g in diam .06 

A4oe # 6 two holes with hole T \ in diam .10 

A4of # 6 one hole .10 

A4og # 6 two holes (one hole at center) 10 

A4oh # 7 three holes at i5ff (2) .30 

A4oi # 7 two holes (one hole at center) 15 

A4oj # 7 two holes at 12^ (2) 24 

A4ok #10 one hole .36 

A4i Rubber tubing, heavy wall, black; EA 6054, SS i27oob, specify 

inside diameter T \ in. 

A4ia 2 pieces 12 in. at 20ff 40 

A4ib 2 pieces 6 in. at ioj 20 



256 LABORATORY PROJECTS IN PHYSICS 

A4ic 3 pieces 4 in. 20 

A4id 6 pieces 2 in 20 

A42 Rubber tubing for Bunsen burner attachments, 2 ft. ; EA #6048 

heavy wall, white or red, inside diam. in., thickness of wall 

i in. at 12^ per ft ,. ,24 

A42a Rubber tubing, special for measuring faucet water pressure, 

inside diam. | in., test 75 to 100 Ibs. per sq. in. ; SS, per foot .20 

A43 Thermometers, Centigrade ; SS or EA or CS i.oo 

A44 Wire, copper, double cotton covered No. 24 ; SS, double cotton 

covered magnet wire at $2.60 per one pound spool ... .05 
A44a Lamp cord insulated copper wire for no volt line; SS N 8000 

lamp cord wire No. 18. 

B. Material Used in One Experiment Only. 

645 The Clock Tick Tack Clock; SS or LK or CS 1.80 

646 Measuring Fluid Pressures Mercury; SS 20 

647 Floating Bodies Lead Sinker, wt. 4 oz., diam. i in., SS or LK .13 
B47a Aluminum pan, quart size Wearever # 168 Pudding Pan, 

Aluminum Cooking Utensil Co., N. Y. or SS 50 

648 Liquid Cell and Dry Cell. 

B48a Base-block 5 in.X5 in.X2 in. with round hole for round 

tumbler battery jar, 5^ in. highX2^ in. bottom diam.; SS . .50 

B48b Battery Jar as described above; SS or L. Straus & Sons, 

44 Warren St., N. Y. In dozen lots, per doz. $2.45 . . . .21 

B48c Ammonium chloride salt (sal ammoniac), technical grade; 

SS or EA in ten pound lots at 20^ 20 

B48d Battery zinc rods (pencil) ; SS or SP 021234 10 

649 Electromagnets and Permanent Magnets. 

B4pa Nails, 12 penny .10 

B4gb Nails, \ Ib, half inch flat head, any hardware store .... .10 

B4QC Steel knitting needles ; SR 10 

B$o Electroplating. 

Copper sheet, 7 in. longXi^ in. wide; SS 10 

Copper sulfate powder or granules technical, any chemical 

supply house in 10 pound lots at 25^ ; Merck & Co., N. Y. .10 
no-volt lamp resistance board with keyless sockets; SS or CS 1.50 
BSI Electric Light and Power. 

Small electric motor (Little Hustler), 3 volt ; CS or LK or SS i .50 
652 Law of Reflection. 

Mirrors, nickel plated (special) ; SS 25 



APPENDIX 257 

653 Law of Intensity. 

Cardboards with holes and with one inch squares for screen ; 

SS 10 

654 Prism and Lens. 

B54a Prism, equilateral, width of face 28 mm., length 75 mm.; 

CS F65U 60 

6540 Protractor, brass ; LK 13-90 .12 

655 Lens and Glass Cube. 

Glass Cube ; LK 74-62, 50 mm. edge .80 

656 Absorption and Light. 

Gelatine Color Films, sheets 8X10 set of red, green, blue; 
SS 7640, at 20^ .60 

65 7 Tuning Fork and Vibrating Column. 

Tuning Fork, 512 vibrations per sec. ; SS Hi 50 1.50 

Bs8 Vibrating String. 

Piano wire, diam. .025 in. (music gauge #10) (B&S #22) 

SS 15385; per meter .05 

B59 Pressure Tank Water System Pump, brass hand pump; SS or 

A. B. Sands & Son, 20 Vesey St., N. Y 2.50 

GROUP II-III EXPERIMENTS 

37 Blood Pressure. 

37A U-tube (use manometer tube Group I.) ; SS 2.50 

376 Arm sleeve, rubber bag, and rubber bulb (pump) ; Taylor Instru- 
ment Companies, Rochester, N. Y 5.00 

38 Camera A. 

38A Premo #8 for plate holder or film pack adapter, with planato- 

graph lens, size 4X5; Eastman Kodak Co., Rochester, N. Y. 15.00 
386 Pin-hole camera ; LK, CS, SS, J86o 65 

39 Electric Motor A. 

3pA St. Louis Motor with electromagnet attachments ; CS or SS. . 4.00 

396 35-ampere battery ammeter (Eveready mounted) ; SS ... 2.50 

39C 2 dry cells 40 cents each . . .80 

40 Fireless Cooker. 

40 A Duplex Fireless Cooker ; CW or see SR 11.25 

4oB Gas burner (stove) ; I. Block & Son, N. Y., #i with star burner . 1.70 

4oC Thermos bottle ; pint size, SS or CS 175 

4oD Copper quart measure ; CS #8394 r 60 

4oE Chemical thermometer, o to 212 F; SS or CS 1.25 

4oF Aluminum saucepan, 4 quart ; CW .* . . 1.21 

4oG 200-c.c. glass graduate ; SS 4705 or CS 65 

s 



258 LABORATORY PROJECTS IN PHYSICS 

41 Gas Stove Burner. 

4iA Gas burner; I. Block & Son, N. Y., #i with star burner .. . . 1.70 
416 Gas meter Large Dial Demonstration Dry Meter, 5 light ; 

American Meter Co., N. Y 18.00 

41 C Screw clamp, pinch cock, Hoffmans; SS medium .25 

4iD Alarm clock, without bell; SR i.oo 

41 E Copper quart measure; CS #8394 1.60 

41 F Enamel- ware kettle, 4 quarts; SR . .55 

4iG Chemical thermometer, o to 212 F; SS or CS 1.25 

42 Gasoline Engine A. 

42 A i Horse power gasoline engine on truck. The feed pipe from 
tank may be disconnected and the engine operated by illumi- 
nating gas by means of rubber tube connection ; SR . . . 52.10 

42B Large glass battery jar,> 6X8 in. ; SS or CS 40 

42 C Induction Coil ; SR, 6Ag234 4.85 

42D 4 dry cells; SP, 40 ^ each 1.60 

42E Ignition bottle; SS or use tall narrow bottle i in. diam. (olive 

bottle). 
42F Magneto generator with small lamp ; CS, F37i$ 5.00 

45 House Gas Supply. 

45 A Gas meter Large Dial Demonstration Dry Meter ; American 

Meter Co., N.Y 18.00 

456 Gas stove burner; I. Block & Son, N. Y., #i with star burner . 1.70 

45 C Laboratory Bunsen burner; EA 1462 i.oo 

45D Gas iron (flatiron) ; SR or CW 2.10 

45E Open flame gas lamp ; LK, 70-90 8b 

46 House Water Supply. 

46A Water Meter for half in. pipe connections ; National Meter 

Co., 299 Broadway, N. Y 16.50 

466 Lever handle stop cock, \ in. pipe ; SR 70 

46C 2-ft. piece flexible garden hose with -in. hose coupling ; SR . . .70 

46D Screw faucet ; SR, Compression Hose Bibb ^-in 78 

46E Compression faucet; SR, Fuller Pattern Plain Bibb, -in., -in. 
pipe, 2 six-in. pieces, i twelve-in. piece, 4 L's, SR, or from 

pipe fitter 70 

46F Gallon measure, tinned iron ; CS 8396 40 

46G Quart measure, tin ; SR 38 

46H Wrench, Auto type, length approximately 9-in ; SR 46 

46! Screw driver, 4-in. blade ; SR 3 



APPENDIX 259 

47 Dew Point. 

47 A Nickel plated beaker ; 88750 1.25 

476 Chemical thermometer, o to 212 F; SS or CS 1.25 

47C Pan for ice ; SR 15 

48 Jackscrew 

48A Jackscrew, i o-in. stand; SR or CW 3.20 

486 50 Ib. weight; SR, Atlas test weight (2), $5.75 each .... 11.50 

48C Spring balance, 64 oz. ; 88,6510 50 

For lever use a piece of iron pipe. 

49 Kerosene Stove. 

4gA Stove, Single Burner Perfection Wick Stove; Cleveland 
Foundry Co., Cleveland, Ohio. Remove tin shield from in- 
side of filler, plug opening to aid in pouring kerosene from 

the tank 5.00 

4pB 2OO-c.c. graduate ; 88, 4705 or CS .65 

4gC Tin or aluminum funnel and tin pan, 3 pints ....... .20 

4gD Four-quart kettle, enamel ware ; SR 55 

49E Chemical thermometer, o to 212 F; SS or CS 1.25 

4gF Copper quart measure ; CS 8394 1.60 

50 Lever and Scales. 

5oA Test weights used in Jackscrew experiment. 

506 Crowbar, 1 6 Ib., pinch-point; SR 1.75 

5oC Spring balance, 30 Ib. ; 886530 1.60 

5oD Beam balance used in Group I experiments. 

5oE Steelyard, 100 Ib. ; CW 1.75 

5oF Wooden Bex ; SS 75 

51 Microscope. 

51 A Reading glass lens; SS K2oo, SR 2^-in. size 1.15 

5iB Short focus double con vex lens; Bausch & Lomb Optical Co., 

Rochester, N. Y., #144 Watchmakers' glass it-in. focus . . i.oo 

51 C Microscope; SR 20 R3399 4-95 

52 Optical Disk. 

52 A Optical Disk Apparatus; SS or CS or LK 16.50 

53 Pressure Cooker. 

53 A Pressure Cooker, 10 qt. size, with pressure thermometer ; SS . . 20.00 

536 Gas burner; I. Block & Son, N. Y., #i with star burner . . . 1.70 



260 LABORATORY PROJECTS IN PHYSICS 

54 Phonograph A. 

54 A Phonograph ; SR, 20 R45oo Junior Silvertone 11.90 

546 Record .75 

54C Tuning Fork, 512 vibrations; SS, #[150 1.50 

S4D Lens 2 in. diam. ; SS or SR 1.20 

54E Screw driver from laboratory tool drawer. 

55 Projection Lantern A. 

55A Projection Lantern, Nitrogen Lamp Type; Bausch & Lomb, 
Rochester, N. Y. Home Balopticon for both opaque pictures 

and lantern slides 45.00 

556 Screen; CS F;545, 6x6 feet 7.00 

55C Ammeter, battery (Eveready) mounted ; SS 2.50 

56 Pulley. 

56 A Pair of Triple Tackle Blocks, one with becket ; SR or CW . . 3.43 
566 Same weights as used in jackscrew. 
56C Same spring balance used in jackscrew. 

57 Pump Kitchen Lift Pump. 

5;A Pitcher spout iron pump with 2^-in. brass lined cylinder; SR 

42R52ooj, CW. Mount on a table using two buckets . . . 3.60 

58 Saucepan Conduction. 

58 A Gas burner; I. Block & Son, N. Y., #i with star burner . . . 1.70 
586 Gas meter, Large Dial Demonstration Meter ; American Meter 

Co, N. Y . I8 .oo 

58C Screw clamp, pinchcock ; Hoff mans, SS medium .25 

58D Copper quart measure ; CS #8394 1.60 

58E Clock without bell; SR i.oo 

58? Four-quart saucepan, enamel ware ; SR .55 

58G Chemical thermometer, o to 200 F; SS or CS 1.25 

58H Saucepan, 4 quarts, aluminum; SR 9R22 23, 4 quarts . . . . 1.45 
58! Saucepan, 4 quarts, copper; Bramhall Dean Co., 261 W. 36th 

St.,N.Y 3.50 

59 Sewing Machine A. 

59A Small hand Singer machine ; Singer* Sewing Machine Co., #20, 

at $3-50- ' 3.SO 

60 Water Motor A. 

6oA Water Motor with Bourdon pressure gauge o to 100 Ib. ; SS . 12.00 

6oB Gallon measure, tinned iron ; CS 8396 .40 

6oC Copper quart measure ; CS 8394 1.60 



APPENDIX 261 

61 Alternating Currents. 

6iA Coils used in Electric Generator. 

6iB Pocket compass; SS N4O5 . . 25 

6iC Large Permanent Magnet SS. Get an old steel file, size i in.X 10 
in. or SR. 

6iD Telephone magneto generator; CS 3715 5.00 

6iE Battery voltmeter, Eveready type o-io volts mounted ; SS . . 2.50 

6iF Electric bell; SS or SR, size gong i\ in 60 

6iG Dry cell any electrical store 40 

63 Camera C. 

63A Negative, plate negative. 

636 Printing Frame, 4X5; SR 2oRi4io .20 

630 Aristo Gold Paper, 4X5; Eastman Kodak Co., Rochester, 

N. Y., per doz. sheets .20 

630 Hypo, or Acid Fixing Powder ; CW, per Ib. . 25 

63E Sal soda (sodium carbonate) ; SS, per Ib .25 

63 F Glass graduate in oz., measuring glass 8 oz. ; SR 15 

63G Glass tray, 4X5; CW 15 

63H White enamel trays (2) ; CW, at 55 cents, 4X5 in i.io 

64 Electrical Disk Stove. 

64A Electric stove or hot plate ; SR 6P8o27|, no volts 7.95 

646 Chemical thermometer, o-2i2 F; SS or CS 1.25 

64C Copper quart measure ; CS #8394 1.60 

640 4 qt. saucepan, enamel ware; SR 55 

64E Gas burner, use burner for Saucepan experiment. 
64F Clock, use one of laboratory alarm clocks. 

65 Electric Generator. 

6sA Generator operated by hand power; LK 97-148, Dissectible 

Hand Power Dynamo and Motor 40.00 

6sC Battery ammeter, Eveready type, 0-35 amperes mounted; SS . 2.50 
6sD Battery voltmeter, Eveready type, o-io volts, mounted; SS . 2.50 

65E Small motor, Little Hustler ; CS or LK or SS 1.50 

6sF Telephone magneto generator, use same generator as in Alternat- 
ing Currents experiment. 

Motor-generator same as used in Electric Motor B, or use 
Large Evans Motor Generator; CS. 



262 LABORATORY PROJECTS IN PHYSICS 

66 Electric Immersion Heater. 

66A Electric immersion heater ; SR, Majestic, 6P8o7g, or SS N6o2o, 

600 watts 4.35 

(This apparatus may be kept with the apparatus for Electric 
Disk Stove experiment.) 

67 Electric Motor B. 

67 A 4 dry cells, any electrical dealer, each 40 cents 1.60 

676 Battery ammeter, Eveready, mounted ; SS 2.50 

67C Generator-Motor, hand power; LK 97-150 Dissectible, use same 

apparatus as in Experiment 65, Electric Generator. Evans 

Motor-generator set, CS, 70, no volt, A. C. or D. C. 

Motor with two armatures for the generator. 
670 Rheostat use rheostat suitable for the motor when attaching 

no- volt line; CS or SS. 
67E Compass; SS 25 

68 Gasoline Engine B. 

Use the engine of Gasoline Engine A. 

69 Horse Power A. 

6gA Universal Electric Motor for either AC or DC, no volts; SS 

Ni384, mounted on ring stand for brake test 10.00 

6gB Right angle clamp ; SS Ai 280, size (b) 75 

6gC Iron Rod 8 in. long, diameter 8mm. ; SS .15 

6gD Spring balances (2) 64 oz., SS 6510, each 50 cents i.oo 

6gE Speed counter; SS 6150 i.oo 

70 Horse Power B 

Same apparatus used in Horse Power A. 
7oA Ammeter for DC current use; SS NiSso, 15 ampere (Weston 

Meter # 167). This meter should be mounted on wood stand 12.50 

72 Humidity B. 

72A Wet and dry bulb hygrometer ; Taylor Instrument Co., Roches- 
ter, N. Y 2.50 

73 Phonograph B 

73A Same instrument used in Phonograph A. 

736 Screw driver ; SR or CW 15 

74 Projection Lantern B. 

74A Carbon arc projection lantern ; Bausch & Lomb Opt. Co., Roches- 
ter, N. Y., #5000 45.00 



APPENDIX 263 

746 Small carbon rods; Bausch & Lomb Opt. Co., 4473, per 10 . . .38 

74C Large carbon rods; Bausch & Lomb Opt. Co., 4470, per 10 . . .40 
74D Five-ampere rheostat, no volts; Bausch & Lomb Opt. Co., 

4452 5-00 

74E Ammeter same as used in Horse Power B. 

74F Single lamp board and one ampere lamp; SS 2.00 

746 1 5-ampere rheostat; Bausch & Lomb Opt. Co., 4450 .... 7.00 

75 The Rheostat. 

75A #30 Nickel chromium alloy; SS, Nichrome resistance wire, one 

pound spool, Hoskins Mfg. Co., Detroit, Mich., per pound 3.75 
756 Rheostat used in Projection Lantern B. 
7$C Ammeter, mounted battery type ; SS 2.50 

76 Sewing Machine B 

76A Buy a used machine or purchase one from SR or CW .... 35.00 

77 The Steam Engine. 

77A Small outfit engine and boiler; LK 69-85 80 

776 Large outfit engine and boiler; LK 69-120 74-5O 

77C Demonstration model; LK 69-30 3.25 

78 Telephone A. 

78A Telephone receivers (3); SR 6R8i65, or SS, each $1.40 . . . 4.20 
786 Telephone transmitters (2); SR 6R8i59, each $1.90 .... 3.80 

78C Wire #18 annunciator; SR 6R9902, one pound .64 

78D Binding posts with wood screw for ends of wires (4) ; SS N57o, 

each 25 cents i.oo 

Extend wires from one room to another if convenient. 
78E Two dry cells, each 40 cents. 

Use No. 24 insulated wire for making attachments ; SS. 

78F Clock without alarm ; SR i.oo 

78G Copper plates (thin) two each one inch square. Punch small 

hole for wire ; SS. 
78H Carbon granules. Break up old projection-lantern carbon and 

keep hi a bottle. 

79 Telephone B 

7gA Short line battery telephone, 2 instruments ; Manhattan Elec- 
trical Supply Co., N. Y., 1561, each $5.00 10.00 

The back should be removable from these phones to show the 
wiring. 

796 Magneto generator, three magnets ; CS F37I5 .,,,,, 5.00 



264 LABORATORY PROJECTS IN PHYSICS 

So Telescope 

8oA Double convex lens in mount reading glass, lens 3 in. diameter ; 

SR . 2.65 

8oB Short focus, double convex lens; Bausch & Lomb Optical Co., 

Rochester, N. Y. #144. Watchmaker's glass i^ hi. focus . i.oo 

8 1 Thermometer. 

8iA Thermometer or barometer tubing, diameter five mm., bore one 

mm.; SS, CS .50 

82 Vacuum Cleaner 

82A Vacuum cleaner centrifugal fan type 40.00 

826 Manometer tube; SS 2.50 

82C Rubber stopper, #7, one-hole; SS 15 

82D Speed indicator same as used in Horse Power A. 

82E Rule, any foot rule. 

82F Ammeter, same as used in Horse Power B. 

826 Rug, one and one half feet by three feet 3.00 

82H Spring Balance, 30 Ib. ; SS 6530 1.60 

82! Screw.driver; SR 15 

83 Water Heater. 

83 A Gas meter. Use meter from House Gas Supply Exp. (41). 

836 Screw clamp, pinch cock, Hoffmans ; SS, medium .... .25 

83C Gas water heater; SR42Rio8ol or SS 5.80 

The water tube ends may be fitted with a reducer to three 
eighths and with brass hose ends for connecting with water 
faucet by means of rubber tubing. A brass hose end should 
also be connected to the gas inlet for convenience in attach- 
ing to gascock. 

Get two galvanized reducers changing from three quarters 
to three eighths size .30 

830 Brass hose ends male (3) ; E. P. Gleason, 37 Murray St., N. Y., 

at .13 .39 

83E Rubber tubing; EA 6048, heavy wall, white, inside diam. J in., 

10 feet at 12 cents . . 1.20 

83F Faucet stopper (rubber) 10 

836 Gallon measure; CS 8396, 40^, or SS, copper plated, 75^ ... .40 

84 Water Motor B. 

84 A Water motor. Use apparatus of Water Motor A. 

846 Two spring balances ; SS B 500, at 8oyf 1.60 

$4C Speed counter same as used in Horse Power A, 



APPENDIX 265 

85 Wireless A 

85 A Two copper aerial wires, each 20 feet of #14 gauge; SR dAggSg^ .40 

856 Spark coil (induction coil) ; SR 6A9234 4.85 

850 Five dry cells at .40 2.00 

85 D Wireless key ; SR 6Ag242 1.29 

85E Aerial insulators (4); SR 6A933S, at 27 cents 1.08 

85? Detector stand; SR 6A92oy 1.95 

850 i ooo-ohm receivers; SR 6 A9440 (meteor) 3.90 

86 Wireless B. 

Aerials same as Wireless A. 

Induction coil same as Wireless A. 

86 A Sending transformer; SR 6A9 244, Standard Helix 2.75 

86B Leyden jar for sending aerial ; SR 6X9202 2.30 

86C Use dry cells and key of Wireless A. 

86D Slide tuner; SR 6A9256, Acme Double Slide Tuner .... 3.10 

86E Fixed condenser ; SR 6 Ag 264. Standard Fixed Cond 60 

86F Variable condenser ; SR 6A923I 3.50 

86G looo-ohm receiver. Use apparatus of Wireless A. 
86H Receiving transformer; SR 6A92i6, Precision Receiving Trans- 
former 7.75 

87 Carburetor A 

87 A Bunsen burner. Use laboratory burner. 

876 Ignition bottle. Use a heavy glass cylinder (olive bottle) or 
hydrometer jar i| in. inside diameter; SS. 

870 Large glass battery jar; SS or SC 40 

870 Sectional carburetor. Get second-hand carburetors from auto- 
mobile dealers and have one or more of them cut open by a 
machinist, or purchase sectional carburetor from manufacturer 10.00 

G3 Carburetor B. 

Same apparatus as for Carburetor A. 

89 Ford Engine A. 

89A Get second-hand Ford car. Remove body and radiator, cylin- 
der head, bottom plate from crank case and one piston from 
crank shaft. Have a blacksmith extend an iron from the 
chassis frame to hold the steering apparatus in place .... 100.00 

90 Ford Engine B. 

Same as Ford Engine A. 



266 LABORATORY PROJECTS IN PHYSICS 

91 Ignition Systems A. 

9iA Four dry cells at 40 cents 1.60 

giB 10 feet of flexible lamp cord wire ; SS NSooo lamp cord wire No. 18 .65 

91 C Induction coil, use coil of Gas Engine A, Experiment 42. 

91 D Automobile spark plugs. Champion; SR .70 

92 Ignition Systems B. 

92A Induction coil. Use apparatus in Ignition Systems A. 

926 Four spark plugs. Champion; SR 2.80 

92C Four ring stands. Use regular laboratory stands and clamps. 

92D Wooden block with four binding posts. Mount four binding 
posts on a block 4 inches square. Binding posts (4) ; SS 
N570, at 25 cents i.oo 

92E Make-and-break coil ; SR 6R95O9 90 

93 Ignition Systems C Ford Ignition. 

93A Ford engine and chassis. 

The Ford induction coil box should be mounted on the chassis 

frame at the left of the engine. 

936 10 feet of flexible lamp cord wire ; SS NSooo lamp cord wire No. 18 .65 
93C 6 dry cells 2.40 

94 Storage Battery A. 

94A Round battery jar 5! in. high by i\ in. bottom diameter in wooden 

base block; SS . . .60 

946 Battery voltmeter, 10 volts (mounted) ; SS 2.50 

94C Battery ammeter, 35-ampere (mounted) ; SS 2.50 

94D Electric bell ; SS 60 

94E 2-volt lamp. Use with lamp socket ; SS .20 

94F Small motor, " Little Hustler," CS; SS Ni362 1.50 

946 Lamp board with one ampere, no-volt lamp; SS Ni475 with 

keyless socket i.oo 

95 Storage Battery B. 

95 A Lead storage cell in glass jar ; CS 1042 No. B 4.40 

956 Battery hydrometer. Floating hydrometer for open type bat- 
teries; Willard Storage Battery Co., Cleveland, O 75 

95C Battery ammeter, mounted ; SS 2.50 

Cabinets for Apparatus 

Cabinet of drawers for storing Group I Materials. For con- 
venience these cabinets should not be higher than five feet; 



APPENDIX 267 

Leonard Peterson & Co., Chicago. Get a quotation on upper 
half of Seed Cabinet, No. 1365 . 

Cabinets for Group II Materials; Kewaunee Mfg. Co., Kewaunee, 

Wis., Nos. 1429, 1430, Leonard Peterson & Co., Chicago, Nos. 
1386, 1387, 1388. 

Valuable pieces of apparatus are stored in a special locker in the instructor's 
office. Students are required to sign a slip of paper with the name of the 
apparatus desired and the date. This slip is kept by the instructor and de- 
livered to the student as a receipt for the apparatus when it is returned. 

A centrally located drawer is assigned for general tools such as screw drivers, 
hammers, wrenches, files, etc. 

Electric Wiring for the Laboratory. 

Provision for electrical experiments with 1 10 volts current is made by extend- 
ing a conduit along a table at the side of the room. This conduit should 
have outlets for attachment plugs three feet apart. For a class of twenty 
students ten outlets should be provided. The laboratory conduit should not 
be attached permanently to the supply lines. It should be connected by 
means of a knife-switch placed in a distribution box. 



Printed in the United States of America, 



<M 



oil 



O- <D = 

T*l ' 
*i; O; 



a 

Oi 

o! j-,i 

oi oi 

Oi rO; 



University of Toronto 
Library 




Acme Library Card Pocket 

Under Pat. "Ref. Index File" 
Made by LIBRARY BUREAU